freepascal.compiler/docs/linux.tex

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\chapter{The LINUX unit.}
\label{ch:linux}

\FPCexampledir{linuxex}
This chapter describes the LINUX unit for Free Pascal. The unit was written
by Micha\"el van Canneyt. It works only on the Linux operating system.
This chapter is divided in 3 sections:
\begin{itemize}
\item The first section lists all constants, types and variables, as listed
in the interface section of the LINUX unit.
\item The second section gives and overview of all available functions,
grouped by category.
\item The third section describes all procedures and functions in the LINUX
unit.
\end{itemize}

% Type, Variable and Constant declarations
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Type, Variable and Constant declarations}

%
\subsection{Types}
\label{sec:types}
PGlob and TGlob are 2 types used in the \seef{Glob} function:
\begin{verbatim}
PGlob = ^TGlob;
TGlob = record
  Name : PChar;
  Next : PGlob;
  end;
\end{verbatim}
The following types are used in the signal-processing procedures.
\begin{verbatim}
tfpreg = record
  significand: array[0..3] of word;
  exponent: word;
end;

pfpstate = ^tfpstate;
tfpstate = record
  cw, sw, tag, ipoff, cssel, dataoff, datasel: cardinal;
  st: array[0..7] of tfpreg;                            
  status: cardinal;
end;

PSigContextRec = ^SigContextRec;
SigContextRec = record
  gs, __gsh: word;
  fs, __fsh: word;
  es, __esh: word;
  ds, __dsh: word;
  edi: cardinal;   
  esi: cardinal;   
  ebp: cardinal;   
  esp: cardinal;   
  ebx: cardinal;   
  edx: cardinal;   
  ecx: cardinal;   
  eax: cardinal;   
  trapno: cardinal;
  err: cardinal;   
  eip: cardinal;   
  cs, __csh: word; 
  eflags: cardinal;
  esp_at_signal: cardinal;
  ss, __ssh: word;
  fpstate: pfpstate;
  oldmask: cardinal;
  cr2: cardinal;
  end;
\end{verbatim}
The above records contain information about the processor state and process
state at the moment a signal is sent to your program.

The records below are used in catching signals.
\begin{verbatim}
TSigAction = procedure(Sig: Longint; SigContext: SigContextRec);cdecl;
SignalHandler   = Procedure ( Sig : Integer);cdecl;

PSignalHandler  = SignalHandler;
SignalRestorer  = Procedure;cdecl;
PSignalrestorer = SignalRestorer;
SigActionRec = packed record
  Handler  : record
    case byte of   
      0: (Sh: SignalHandler);
      1: (Sa: TSigAction);   
    end;
  Sa_Mask     : SigSet;
  Sa_Flags    : Longint;
  Sa_restorer : SignalRestorer; { Obsolete - Don't use }
end;
  PSigActionRec = ^SigActionRec;
\end{verbatim}
Stat is used to store information about a file. It is defined in the
syscalls unit.
\begin{verbatim}
  stat = record
     dev    : word;
     pad1   : word;
     ino    : longint;
     mode   : word;
     nlink  : word;
     uid    : word;
     gid    : word;
     rdev   : word;
     pad2   : word;
     size   : longint;
     blksze : Longint;
     blocks : Longint;
     atime  : Longint;
     unused1 : longint;
     mtime   : Longint;
     unused2 : longint;
     ctime   : Longint;
     unused3 : longint;
     unused4 : longint;
     unused5 : longint;
     end;
 \end{verbatim}
Statfs is used to store information about a filesystem. It is defined in
the syscalls unit.
\begin{verbatim}
   statfs = record
     fstype   : longint;
     bsize    : longint;
     blocks   : longint;
     bfree    : longint;
     bavail   : longint;
     files    : longint;
     ffree    : longint;
     fsid     : longint;
     namelen  : longint; 
     spare    : array [0..6] of longint;
     end
\end{verbatim}
\var{Dir and PDir} are used in the \seef{OpenDir} and \seef{ReadDir}
functions. 
\begin{verbatim}
  TDir =record
    fd     : integer;
    loc    : longint;
    size   : integer;
    buf    : pdirent;
    nextoff: longint;
    dd_max : integer; 
    lock   : pointer;
  end;
  PDir =^TDir;
\end{verbatim}
\var{Dirent, PDirent} are used in the \seef{ReadDir} function to return files in a directory.
\begin{verbatim}
 PDirent = ^Dirent;
 Dirent = Record  
   ino,
   off    : longint;
   reclen : word;
   name   : string[255]
 end; 
\end{verbatim}
Termio and Termios are used with iotcl() calls for terminal handling.
\begin{verbatim}
Const  NCCS = 19;
       NCC = 8;
         
Type termio = record
	c_iflag,		{ input mode flags }
	c_oflag,		{ output mode flags }
	c_cflag,		{ control mode flags }
	c_lflag : Word;		{ local mode flags }
	c_line : Word;		{ line discipline - careful, only High byte in use}
	c_cc : array [0..NCC-1] of char;	{ control characters }
end;
termios = record
  c_iflag,              { input mode flags }
  c_oflag,              { output mode flags }
  c_cflag,              { control mode flags }
  c_lflag : Cardinal;	{ local mode flags }
  c_line : char;          { line discipline }
  c_cc : array [0..NCCS-1] of char;      { control characters }
end;
\end{verbatim}
\var{Utimbuf} is used in the \seef{Utime} call to set access and modificaton time
of a file.
\begin{verbatim}
utimbuf = record
  actime,modtime : Longint;
  end;
\end{verbatim}
For the \seef{Select} call, the following 4 types are needed:
\begin{verbatim}
FDSet = Array [0..31] of longint;
PFDSet = ^FDSet;
TimeVal = Record
   sec,usec : Longint;
end;
PTimeVal = ^TimeVal;
\end{verbatim}
The \var{timespec} record is needed in the \seef{NanoSleep} function:
\begin{verbatim}
timespec = packed record
  tv_sec,tv_nsec:longint;
end;
\end{verbatim}

The \seep{Uname} function uses the \var{utsname} to return information about
the current kernel :
\begin{verbatim}
utsname =record
  sysname,nodename,release,
  version,machine,domainname : Array[0..64] of char;
end;
\end{verbatim}
Its elements are null-terminated C style strings, you cannot access them
directly !

%
\subsection{Variables}
\var{Linuxerror} is the variable in which the procedures in the linux unit
report errors.
\begin{verbatim}
LinuxError : Longint;
\end{verbatim}
\var{StdErr} Is a \var{Text} variable, corresponding to Standard Error or
diagnostic output. It is connected to file descriptor 2. It can be freely
used, and will be closed on exit.
\begin{verbatim}
StdErr : Text;
\end{verbatim}

%
\subsection{Constants}
Constants for setting/getting process priorities :
\begin{verbatim}
      Prio_Process = 0;
      Prio_PGrp    = 1;
      Prio_User    = 2;
\end{verbatim}
For testing  access rights:
\begin{verbatim}
      R_OK = 4; 
      W_OK = 2;
      X_OK = 1;
      F_OK = 0;
\end{verbatim}
For signal handling functions :
\begin{verbatim}
      SA_NOCLDSTOP = 1;
      SA_SHIRQ	   = $04000000;
      SA_STACK	   = $08000000;      
      SA_RESTART   = $10000000;
      SA_INTERRUPT = $20000000;
      SA_NOMASK	   = $40000000;
      SA_ONESHOT   = $80000000;
      
      SIG_BLOCK	  = 0;
      SIG_UNBLOCK = 1;
      SIG_SETMASK = 2;
      SIG_DFL = 0 ;
      SIG_IGN = 1 ;
      SIG_ERR = -1;
      
      SIGHUP		= 1;
      SIGINT		= 2;
      SIGQUIT		= 3;
      SIGILL		= 4;
      SIGTRAP		= 5;
      SIGABRT		= 6;
      SIGIOT		= 6;
      SIGBUS		= 7;
      SIGFPE		= 8;
      SIGKILL		= 9;
      SIGUSR1		= 10;
      SIGSEGV		= 11;
      SIGUSR2		= 12;
      SIGPIPE		= 13;
      SIGALRM		= 14;
      SIGTERM		= 15;
      SIGSTKFLT		= 16;
      SIGCHLD		= 17;
      SIGCONT		= 18;
      SIGSTOP		= 19;
      SIGTSTP		= 20;
      SIGTTIN		= 21;
      SIGTTOU		= 22;
      SIGURG		= 23;
      SIGXCPU		= 24;
      SIGXFSZ		= 25;
      SIGVTALRM		= 26;
      SIGPROF		= 27;
      SIGWINCH		= 28;
      SIGIO		= 29;
      SIGPOLL		= SIGIO;
      SIGPWR		= 30;
      SIGUNUSED		= 31;
\end{verbatim}
For file control mechanism :
\begin{verbatim}
      F_GetFd  = 1;
      F_SetFd  = 2;
      F_GetFl  = 3;
      F_SetFl  = 4;
      F_GetLk  = 5;
      F_SetLk  = 6;
      F_SetLkW = 7;
      F_GetOwn = 8;
      F_SetOwn = 9;
\end{verbatim}
For Terminal handling :
\begin{verbatim}
   TCGETS	= $5401 ;
   TCSETS	= $5402 ;
   TCSETSW	= $5403 ;
   TCSETSF	= $5404 ;
   TCGETA	= $5405 ;
   TCSETA	= $5406 ;
   TCSETAW	= $5407 ;
   TCSETAF	= $5408 ;
   TCSBRK	= $5409 ;
   TCXONC	= $540A ;
   TCFLSH	= $540B ;
   TIOCEXCL	= $540C ;
   TIOCNXCL	= $540D ;
   TIOCSCTTY	= $540E ;
   TIOCGPGRP	= $540F ;
   TIOCSPGRP	= $5410 ;
   TIOCOUTQ	= $5411 ;
   TIOCSTI	= $5412 ;
   TIOCGWINSZ	= $5413 ;
   TIOCSWINSZ	= $5414 ;
   TIOCMGET	= $5415 ;
   TIOCMBIS	= $5416 ;
   TIOCMBIC	= $5417 ;
   TIOCMSET	= $5418 ;
   TIOCGSOFTCAR	= $5419 ;
   TIOCSSOFTCAR	= $541A ;
   FIONREAD	= $541B ;
   TIOCINQ	= FIONREAD;
   TIOCLINUX	= $541C ;
   TIOCCONS	= $541D ;
   TIOCGSERIAL	= $541E ;
   TIOCSSERIAL	= $541F ;
   TIOCPKT	= $5420 ;
   FIONBIO	= $5421 ;
   TIOCNOTTY	= $5422 ;
   TIOCSETD	= $5423 ;
   TIOCGETD	= $5424 ;
   TCSBRKP		= $5425	 ;
   TIOCTTYGSTRUCT	= $5426  ;
   FIONCLEX	= $5450  ;
   FIOCLEX		= $5451 ;
   FIOASYNC	= $5452 ;
   TIOCSERCONFIG	= $5453 ;
   TIOCSERGWILD	= $5454 ;
   TIOCSERSWILD	= $5455 ;
   TIOCGLCKTRMIOS	= $5456 ;
   TIOCSLCKTRMIOS	= $5457 ;
   TIOCSERGSTRUCT	= $5458  ;
   TIOCSERGETLSR   = $5459  ;
   TIOCSERGETMULTI = $545A  ;
   TIOCSERSETMULTI = $545B  ;
   TIOCMIWAIT	= $545C	;
   TIOCGICOUNT	= $545D	;
   TIOCPKT_DATA		= 0;
   TIOCPKT_FLUSHREAD	= 1;
   TIOCPKT_FLUSHWRITE	= 2;
   TIOCPKT_STOP		= 4;
   TIOCPKT_START	= 8;
   TIOCPKT_NOSTOP	= 16;
   TIOCPKT_DOSTOP	= 32;
\end{verbatim}
Other than that, all constants for setting the speed and control flags of a
terminal line, as described in the \seem{termios}{2} man
page, are defined in the linux unit. It would take too much place to list
them here. 
To check the \var{mode} field of a \var{stat} record, you ca use the
following constants :
\begin{verbatim}
  { Constants to check stat.mode }
  STAT_IFMT   = $f000; {00170000}
  STAT_IFSOCK = $c000; {0140000}
  STAT_IFLNK  = $a000; {0120000}
  STAT_IFREG  = $8000; {0100000}
  STAT_IFBLK  = $6000; {0060000}
  STAT_IFDIR  = $4000; {0040000}
  STAT_IFCHR  = $2000; {0020000}
  STAT_IFIFO  = $1000; {0010000}
  STAT_ISUID  = $0800; {0004000}
  STAT_ISGID  = $0400; {0002000}
  STAT_ISVTX  = $0200; {0001000}
  { Constants to check permissions }
  STAT_IRWXO = $7;
  STAT_IROTH = $4;
  STAT_IWOTH = $2;
  STAT_IXOTH = $1;
  STAT_IRWXG = STAT_IRWXO shl 3;
  STAT_IRGRP = STAT_IROTH shl 3;
  STAT_IWGRP = STAT_IWOTH shl 3;
  STAT_IXGRP = STAT_IXOTH shl 3;
  STAT_IRWXU = STAT_IRWXO shl 6;
  STAT_IRUSR = STAT_IROTH shl 6;
  STAT_IWUSR = STAT_IWOTH shl 6;
  STAT_IXUSR = STAT_IXOTH shl 6;
\end{verbatim}
You can test the type of a filesystem returned by a \seef{FSStat} call with
the following constants:
\begin{verbatim}
  fs_old_ext2 = $ef51;
  fs_ext2     = $ef53;
  fs_ext      = $137d;
  fs_iso      = $9660;
  fs_minix    = $137f;
  fs_minix_30 = $138f;
  fs_minux_V2 = $2468;
  fs_msdos    = $4d44;
  fs_nfs      = $6969;
  fs_proc     = $9fa0;
  fs_xia      = $012FD16D;
\end{verbatim}
the \seef{FLock} call uses the following mode constants :
\begin{verbatim}
  LOCK_SH = 1;
  LOCK_EX = 2;
  LOCK_UN = 8;
  LOCK_NB = 4;
\end{verbatim}
The \seef{MMap} function uses the following constants to specify access to
mapped memory:
\begin{verbatim}
  PROT_READ  = $1;   { page can be read }
  PROT_WRITE = $2;   { page can be written } 
  PROT_EXEC  = $4;   { page can be executed }
  PROT_NONE  = $0;   { page can not be accessed }
\end{verbatim}
and the following constants to specify the type of mapping.
\begin{verbatim}
  MAP_SHARED    = $1;  { Share changes }
  MAP_PRIVATE   = $2;  { Changes are private }
  MAP_TYPE      = $f;  { Mask for type of mapping }
  MAP_FIXED     = $10; { Interpret addr exactly }
  MAP_ANONYMOUS = $20; { don't use a file }
\end{verbatim}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Functions and procedures by category
\section{Function list by category}
What follows is a listing of the available functions, grouped by category.
For each function there is a reference to the page where you can find the
function.
\subsection{File Input/Output routines}
Functions for handling file input/output.
\begin{funclist}
\funcref{Dup}{Duplicate a file handle}
\funcref{Dup2}{Copy one file handle to another}
\procref{Fcntl}{General file control}
\funcref{fdClose}{Close file descriptor}
\funcref{fdFlush}{Flush file descriptor}
\funcref{fdOpen}{Open new file descriptor}
\funcref{fdRead}{Read from file descriptor}
\funcref{fdSeek}{Position in file}
\funcref{fdTruncate}{Truncate file}
\funcref{fdWrite}{Write to file descriptor}
\funcref{GetFS}{Get file descriptor of pascal file}
\funcref{Select}{Wait for input from file descriptor}
\funcref{SelectText}{Wait for input from pascal file}
\end{funclist}

\subsection{General File handling routines}
Functions for handling files on disk.
\begin{funclist}
\funcref{Access}{Check access rights on file}
\funcref{BaseName}{Return name part of file}
\funcref{Chown}{Change owner of file}
\funcref{Chmod}{Change access rights on file}
\funcref{DirName}{Return directory part of file}
\procrefl{FSplit}{LFsplit}{Split filename in parts}
\funcref{FExpand}{Return full-grown filename}
\funcref{FLock}{Set lock on a file}
\funcref{FNMatch}{Match filename to searchpattern}
\funcref{FSearch}{Search for a file in a path}
\funcref{FSStat}{Return filesystem information}
\funcref{FStat}{Return file information}
\funcref{FRename}{Rename file}
\funcref{LStat}{Return information on a link}
\funcref{Link}{Create a link}
\funcref{ReadLink}{Read contents of a symbolic link}
\funcref{SymLink}{Create a symbolic link}
\funcref{Umask}{Set the file creation mask}
\funcref{UnLink}{Remove a file}
\funcref{Utime}{Change file timestamps}
\end{funclist}

\subsection{Pipes, FIFOs and streams }
Functions for creating and managing pipes.
\begin{funclist}
\funcref{AssignPipe}{Create a pipe}
\funcref{AssignStream}{Create pipes to program's input and output}
\funcref{MkFifo}{Make a fifo}
\funcref{PClose}{Close a pipe}
\procref{POpen}{Open a pipe for to program's input or output}
\end{funclist}

\subsection{Directory handling routines}
Functions for reading and searching directories.
\begin{funclist}
\funcref{CloseDir}{Close directory handle}
\funcref{Glob}{Return files matching a search expression}
\procref{GlobFree}{Free result of Glob}
\funcref{OpenDir}{Open directory for reading}
\funcref{ReadDir}{Read directory entry}
\procref{SeekDir}{Seek directory}
\funcref{TellDir}{Seek directory}
\end{funclist}

\subsection{Process handling}
Functions for managing processes and programs.
\begin{funclist}
\funcref{Clone}{Create a thread}
\procref{Execl}{Execute process with command-line list}
\procref{Execle}{Execute process with command-line list and environment}
\procref{Execlp}{Search in path and execute process with command list}
\procref{Execv}{Execute process}
\procref{Execve}{Execute process with environment}
\procref{Execvp}{Search in path and execute process}
\funcref{Fork}{Spawn child process}
\funcref{GetEGid}{Get effective group id}
\funcref{GetEnv}{Get environment variable}
\funcref{GetEUid}{Get effective user id}
\funcref{GetGid}{Get group id}
\funcref{GetPid}{Get process id}
\funcref{GetPPid}{Get parent process id}
\funcref{GetPriority}{Get process priority}
\funcref{GetUid}{Get user id}
\procref{Nice}{Change priority of process}
\funcref{SetPriority}{Change priority of process}
\funcref{Shell}{Execute shell command}
\funcref{WaitPid}{Wait for child process to terminate}
\end{funclist}

\subsection{Signals}
Functions for managing and responding to signals.
\begin{funclist}
\funcref{Alarm}{Send alarm signal to self}
\funcref{Kill}{Send arbitrary signal to process}
\procref{pause}{Wait for signal to arrive}
\procref{SigAction}{Set signal action}
\funcref{Signal}{Set signal action}
\funcref{SigPending}{See if signals are waiting}
\procref{SigProcMask}{Set signal processing mask}
\procref{SigRaise}{Send signal to self}
\procref{SigSuspend}{Sets signal mask and waits for signal}
\funcref{NanoSleep}{Waits for a specific amount of time}
\end{funclist}

\subsection{System information}
Functions for retrieving system information such as date and time.
\begin{funclist}
\procref{GetDate}{Return system date}
\procref{GetDateTime}{Return system date and time}
\funcref{GetDomainName}{Return system domain name}
\funcref{GetEpochTime}{Return epoch time}
\funcref{GetHostName}{Return system host name}
\procref{GetLocalTimezone}{Return system timezone}
\procref{GetTime}{Return system time}
\funcref{GetTimeOfDay}{Return system time}
\funcref{GetTimezoneFile}{Return name of timezone file}
\procref{ReadTimezoneFile}{Read timezone file contents}
\funcref{SysInfo}{Return general system information}
\procref{Uname}{Return system information}
\end{funclist}

\subsection{Terminal functions}
Functions for controlling the terminal to which the process is connected.

\begin{funclist}
\procref{CFMakeRaw}{Set terminal to raw mode}
\procref{CFSetISpeed}{Set terminal reading speed}
\procref{CFSetOSpeed}{Set terminal writing speed}
\procref{IOCtl}{General IO control call}
\funcref{IsATTY}{See if filedescriptor is a terminal}
\funcref{TCDrain}{Wait till all output was written}
\funcref{TCFlow}{Suspend transmission or receipt of data}
\funcref{TCFlush}{Discard data written to terminal}
\funcref{TCGetAttr}{Get terminal attributes}
\funcref{TCGetPGrp}{Return PID of foreground process}
\funcref{TCSendBreak}{Send data for specific time}
\funcref{TCSetAttr}{Set terminal attributes}
\funcref{TCSetPGrp}{Set foreground process}
\funcref{TTYName}{Name of tty file}
\end{funclist}

\subsection{Port input/output}
Functions for reading and writing to the hardware ports.
\begin{funclist}
\funcref{IOperm}{Set permissions for port access}
\procref{ReadPort}{Read data from port}
\procref{ReadPortB}{Read 1 byte from port}
\procref{ReadPortL}{Read 4 bytes from port}
\procref{ReadPortW}{Read 2 bytes from port}
\procref{WritePort}{Write data to port}
\procref{WritePortB}{Write 1 byte to port}
\procref{WritePortL}{Write 4 bytes to port}
\procref{WritePortW}{Write 2 bytes to port}
\end{funclist}

\subsection{Utility routines}
Auxiliary functions that are useful in connection with the other functions.
\begin{funclist}
\funcref{CreateShellArgV}{Create an array of pchars from string}
\procref{EpochToLocal}{Convert epoch time to local time}
\procrefl{FD\_Clr}{FDClr}{Clear item of select filedescriptors}
\funcrefl{FD\_IsSet}{FDIsSet}{Check item of select filedescriptors}
\procrefl{FD\_Set}{FDSet}{Set item of select filedescriptors}
\procrefl{FD\_ZERO}{FDZero}{Clear all items in select filedecriptors}
\funcref{LocalToEpoch}{Convert local time to epoch time}
\funcref{MMap}{Map a file into memory}
\funcref{MUnMap}{Unmap previously mapped memory file}
\funcref{Octal}{Convert octal to digital}
\funcrefl{S\_ISBLK}{ISBLK}{Check file mode for block device}
\funcrefl{S\_ISCHR}{ISCHR}{Check file mode for character device}
\funcrefl{S\_ISDIR}{ISDIR}{Check file mode for directory}
\funcrefl{S\_ISFIFO}{ISFIFO}{Check file mode for FIFO}
\funcrefl{S\_ISLNK}{ISLNK}{Check file mode for symboloc link}
\funcrefl{S\_ISREG}{ISREG}{Check file mode for regular file}
\funcrefl{S\_ISSOCK}{ISSOCK}{Check file mode for socket}
\funcref{StringToPPchar}{Create an array of pchars from string}
\end{funclist}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Functions and procedures
\section{Functions and procedures}

\begin{function}{Access}
\Declaration
Function Access (Path : Pathstr; Mode : integer) : Boolean;
\Description
Tests user's access rights on the specified file. Mode is a mask existing of
one or more of
\begin{description}
\item[R\_OK] User has read rights.
\item[W\_OK] User has write rights.
\item[X\_OK] User has execute rights.
\item[F\_OK] User has search rights in the directory where the file is.
\end{description}
The test is done with the real user ID, instead of the effective user ID.
If access is denied, or an error occurred, false is returned.
\Errors
 \var{LinuxError} is used to report errors:
\begin{description}
\item[sys\_eaccess] The requested access is denied, either to the file or one
of the directories in its path.
\item[sys\_einval] \var{Mode} was incorrect.
\item[sys\_enoent] A directory component in \var{Path} doesn't exist or is a
dangling symbolic link.
\item[sys\_enotdir] A directory component in \var{Path} is not a directory.
\item[sys\_enomem] Insufficient kernel memory.
\item[sys\_eloop] \var{Path} has a circular symbolic link.
\end{description}

\SeeAlso
\seef{Chown}, \seef{Chmod}, \seem{Access}{2} 
\end{function}


\FPCexample{ex26}


\begin{function}{Alarm}
\Declaration
Function Alarm(Sec : longint) : Longint;
\Description
Alarm schedules an alarm signal to be delivered to your process in \var{Sec}
seconds. When \var{Sec} seconds have elapsed, Linux will send a \var{SIGALRM}
signal to the current process.  If \var{Sec} is zero, then no new alarm will
be set. Whatever the value of \var{Sec}, any previous alarm is cancelled.

The function returns the number of seconds till the previously scheduled
alarm was due to be delivered, or zero if there was none.
\Errors{None}
\end{function}


\FPCexample{ex59}


\begin{function}{AssignPipe}
\Declaration
Function  AssignPipe(var pipe\_in,pipe\_out:longint):boolean;
Function  AssignPipe(var pipe\_in,pipe\_out:text):boolean;
Function  AssignPipe(var pipe\_in,pipe\_out:file):boolean;
\Description
\var{AssignePipe} creates a pipe, i.e. two file objects, one for input, 
one for output. What is written to \var{Pipe\_out}, can be read from 
\var{Pipe\_in}. 

This call is overloaded. The in and out pipe can take three forms:
an typed or untyped file, a text file or a file descriptor.

If a text file is passed then reading and writing from/to the pipe 
can be done through the usual \var{Readln(Pipe\_in,...)} and
\var{Writeln (Pipe\_out,...)} procedures.

The function returns \var{True} if everything went succesfully,
\var{False} otherwise.
\Errors
In case the function fails and returns \var{False}, \var{LinuxError} 
is used to report errors:
\begin{description}
\item[sys\_emfile] Too many file descriptors for this process.
\item[sys\_enfile] The system file table is full.
\end{description}
\SeeAlso
\seep{POpen}, \seef{MkFifo}, \seem{pipe}{2}
\end{function}


\FPCexample{ex36}


\begin{function}{AssignStream}
\Declaration
Function AssignStream(Var StreamIn,Streamout:text;
                      Const Prog:String) : longint;
Function AssignStream(var StreamIn, StreamOut, StreamErr: Text; 
                      const prog: String): LongInt;
\Description
\var{AssignStream} creates a 2 or 3 pipes, i.e. two (or three) file objects, one for 
input, one for output,(and one for standard error) the other ends of these 
pipes are connected to standard input and output (and standard error) of 
\var{Prog}. \var{Prog} is the name of a program (including path) with options,
 which will be executed.

What is written to \var{StreamOut}, will go to the standard input of
\var{Prog}. Whatever is written by \var{Prog} to it's standard output 
can be read from \var{StreamIn}. 
Whatever is written by \var{Prog} to it's standard error read from 
\var{StreamErr}, if present. 

Reading and writing happens through the usual \var{Readln(StreamIn,...)} and
\var{Writeln (StreamOut,...)} procedures.

{\em Remark:} You should {\em not} use \var{Reset} or \var{Rewrite} on a 
file opened with \var{POpen}. This will close the file before re-opening 
it again, thereby closing the connection with the program.

The function returns the process ID of the spawned process, or -1 in case of
error.

\Errors
In case of error (return value -1) \var{LinuxError} is used to report 
errors:
\begin{description}
\item[sys\_emfile] Too many file descriptors for this process.
\item[sys\_enfile] The system file table is full.
\end{description}
Other errors include the ones by the fork and exec programs
\SeeAlso
\seef{AssignPipe}, \seep{POpen},\seem{pipe}{2}
\end{function}


\FPCexample{ex38}


\begin{function}{BaseName}
\Declaration
Function BaseName (Const Path;Const Suf : Pathstr) : Pathstr;
\Description
Returns the filename part of \var{Path}, stripping off \var{Suf} if it
exists.
The filename part is the whole name if \var{Path} contains no slash,
or the part of \var{Path} after the last slash.
The last character of the result is not a slash, unless the directory is the
root directory.

\Errors
None.
\SeeAlso
\seef{DirName}, \seef{FExpand}, \seem{Basename}{1}
\end{function}

\FPCexample{ex48}

\begin{procedure}{CFMakeRaw}
\Declaration
Procedure CFMakeRaw (var Tios:TermIOS);
\Description
 \var{CFMakeRaw}
  Sets the flags in the \var{Termios} structure \var{Tios} to a state so that 
  the terminal will function in Raw Mode.

\Errors
None.
\SeeAlso
 \seep{CFSetOSpeed}, \seep{CFSetISpeed}, \seem{termios}{2}
\end{procedure}
For an example, see \seef{TCGetAttr}.

\begin{procedure}{CFSetISpeed}
\Declaration
Procedure CFSetISpeed (var Tios:TermIOS;Speed:Longint);
\Description
 \var{CFSetISpeed}
  Sets the input baudrate in the \var{TermIOS} structure \var{Tios} to 
  \var{Speed}.

\Errors
None.
\SeeAlso
\seep{CFSetOSpeed}, \seep{CFMakeRaw}, \seem{termios}{2}
\end{procedure}

\begin{procedure}{CFSetOSpeed}
\Declaration
Procedure CFSetOSpeed (var Tios:TermIOS;Speed:Longint);
\Description
 \var{CFSetOSpeed}
  Sets the output baudrate in the \var{Termios} structure \var{Tios} to
  \var{Speed}.

\Errors
None.
\SeeAlso
\seep{CFSetISpeed}, \seep{CFMakeRaw}, \seem{termios}{2}
\end{procedure}

\begin{function}{Chown}
\Declaration
Function Chown (Path : Pathstr;NewUid,NewGid : Longint) : Boolean;
\Description
 \var{Chown} sets the User ID and Group ID of the file in \var{Path} to \var{NewUid,
NewGid}.
The function returns \var{True} if the call was succesfull, \var{False} if the call
failed.
\Errors
Errors are returned in \var{LinuxError}.
\begin{description}
\item[sys\_eperm] The effective UID doesn't match the ownership of the file,
and is not zero. Owner or group were not specified correctly.
\item[sys\_eaccess] One of the directories in \var{Path} has no
search (=execute) permission.
\item[sys\_enoent] A directory entry in \var{Path} does
not exist or is a symbolic link pointing to a non-existent directory.
\item[sys\_enotdir] A directory entry in \var{OldPath} or \var{NewPath} is
nor a directory.
\item[sys\_enomem] Insufficient kernel memory.
\item[sys\_erofs] The file is on a read-only filesystem.
\item[sys\_eloop] \var{Path} has a reference to a circular
symbolic link, i.e. a symbolic link, whose expansion points to itself.
\end{description}
\SeeAlso
\seef{Chmod}, \seef{Access}, \seem{Chown}(2)
\end{function}

\FPCexample{ex24}

\begin{function}{Chmod}
\Declaration
Function Chmod (Path : Pathstr;NewMode : Longint) : Boolean;
\Description
 \var{Chmod}
Sets the Mode bits of the file in \var{Path} to \var{NewMode}. Newmode can be
specified by 'or'-ing the following:
\begin{description}
\item[S\_ISUID] Set user ID on execution.
\item[S\_ISGID] Set Group ID on execution.
\item[S\_ISVTX] Set sticky bit.
\item[S\_IRUSR] Read by owner.
\item[S\_IWUSR] Write by owner.
\item[S\_IXUSR] Execute by owner.
\item[S\_IRGRP] Read by group.
\item[S\_IWGRP] Write by group.
\item[S\_IXGRP] Execute by group.
\item[S\_IROTH] Read by others.
\item[S\_IWOTH] Write by others.
\item[S\_IXOTH] Execute by others.
\item[S\_IRWXO] Read, write, execute by others.
\item[S\_IRWXG] Read, write, execute by groups.
\item[S\_IRWXU] Read, write, execute by user.
\end{description}

\Errors
Errors are returned in \var{LinuxError}.
\begin{description}
\item[sys\_eperm] The effective UID doesn't match the ownership of the file,
and is not zero. Owner or group were not specified correctly.
\item[sys\_eaccess] One of the directories in \var{Path} has no
search (=execute) permission.
\item[sys\_enoent] A directory entry in \var{Path} does
not exist or is a symbolic link pointing to a non-existent directory.
\item[sys\_enotdir] A directory entry in \var{OldPath} or \var{NewPath} is
nor a directory.
\item[sys\_enomem] Insufficient kernel memory.
\item[sys\_erofs] The file is on a read-only filesystem.
\item[sys\_eloop] \var{Path} has a reference to a circular
symbolic link, i.e. a symbolic link, whose expansion points to itself.
\end{description}

\SeeAlso
\seef{Chown}, \seef{Access}, \seem{Chmod}(2), \seef{Octal}
\end{function}

\FPCexample{ex23}

\begin{function}{Clone}
\Declaration
TCloneFunc=function(args:pointer):longint;cdecl;
Clone(func:TCloneFunc;sp:pointer;flags:longint;args:pointer):longint;
\Description
Clone creates a child process which is a copy of the parent process, just
like \seef{Fork} does. In difference with \var{Fork}, however, the child
process shares some parts of it's execution context with its parent, so it
is suitable for the implementation of threads: many instances of a program
that share the same memory.

When the child process is created, it starts executing the function
\var{Func}, and passes it \var{Args}. The return value of \var{Func} is 
either the explicit return value of the function, or the exit code of
the child process.

The \var{sp} pointer points to the memory reserved as stack space for the
child process. This address should be the top of the memory block to be used
as stack.

The \var{Flags} determine the behaviour of the \var{Clone} call. The low
byte of the Flags contains the number of the signal that will be  sent to 
the parent when  the child dies. 
This may be bitwise OR'ed with the following constants:
\begin{description}
\item[CLONE\_VM] Parent and child share the same memory space, including
memory (un)mapped with subsequent \var{mmap} calls.
\item[CLONE\_FS] Parent and child have the same view of the filesystem;
the \var{chroot}, \var{chdir} and \var{umask} calls affect both processes.
\item[CLONE\_FILES] the file descriptor table of parent and child is shared. 
\item[CLONE\_SIGHAND] the parent and child share the same table of signal
handlers. The signal masks are different, though.
\item[CLONE\_PID] PArent and child have the same process ID.
\end{description}

Clone returns the process ID in the parent process, and -1 if an error
occurred.
\Errors
On error, -1 is returned to the parent, and no child is created.
\begin{description}
\item [sys\_eagain] Too many processes are running.
\item [sys\_enomem] Not enough memory to create child process.
\end{description}
\SeeAlso
\seef{Fork}, \seem{clone}{2}
\end{function}

\FPCexample{ex71}

\begin{function}{CloseDir}
\Declaration
Function CloseDir (p:pdir) : integer;
\Description
 \var{CloseDir} closes the directory pointed to by \var{p}.
It returns zero if the directory was closed succesfully, -1 otherwise.
\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{OpenDir}, \seef{ReadDir}, \seep{SeekDir}, \seef{TellDir},
\seem{closedir}{3}
\end{function}
For an example, see \seef{OpenDir}.

\begin{function}{CreateShellArgV}
\Declaration
function  CreateShellArgV(const prog:string):ppchar;
function  CreateShellArgV(const prog:Ansistring):ppchar;
\Description
\var{CreateShellArgV} creates an array of 3 \var{PChar} pointers that can
be used as arguments to \var{ExecVE} the first elements in the array 
will contain  \var{/bin/sh}, the second will contain \var{-c}, and the third
will contain \var{prog}.

The function returns a pointer to this array, of type \var{PPChar}.
\Errors
None.
\SeeAlso
\seef{Shell}
\end{function}

\FPCexample{ex61}

\begin{function}{DirName}
\Declaration
Function DirName (Const Path : Pathstr) : Pathstr;
\Description
Returns the directory part of \var{Path}.
The directory is the part of \var{Path} before the last slash,
or empty if there is no slash.
The last character of the result is not a slash, unless the directory is the
root directory.

\Errors
None.
\SeeAlso
\seef{BaseName}, \seef{FExpand}, \seem{Dirname}{1}
\end{function}

\FPCexample{ex47}


\begin{function}{Dup}
\Declaration
Function  Dup(oldfile:longint;var newfile:longint):Boolean;
Function  Dup(var oldfile,newfile:text):Boolean;
Function  Dup(var oldfile,newfile:file):Boolean;
\Description
Makes \var{NewFile} an exact copy of \var{OldFile}, after having flushed the
buffer of \var{OldFile} in case it is a Text file or untyped file. 
Due to the buffering mechanism of Pascal, this has not the same functionality
as the \seem{dup}{2} call in C. The internal Pascal buffers are not the same 
after this call, but when the buffers are flushed (e.g. after output), 
the output is sent to the same file.
Doing an lseek will, however, work as in C, i.e. doing a lseek will change 
the fileposition in both files.

The function returns \var{False} in case of an error, \var{True} if
successful.
\Errors
In case of errors, \var{Linuxerror} is used to report errors.
\begin{description}
\item[sys\_ebadf] \var{OldFile} hasn't been assigned.
\item[sys\_emfile] Maximum number of open files for the process is reached.
\end{description}
\SeeAlso
\seef{Dup2}, \seem{Dup}{2} 
\end{function}


\FPCexample{ex31}


\begin{function}{Dup2}
\Declaration
Function  Dup2(oldfile,newfile:longint):Boolean;
Function  Dup2(var oldfile,newfile:text):Boolean;
Function  Dup2(var oldfile,newfile:file):Boolean;
\Description
Makes \var{NewFile} an exact copy of \var{OldFile}, after having flushed the
buffer of \var{OldFile} in the case of text or untyped files. 

\var{NewFile} can be an assigned file. If \var{newfile} was open, it is 
closed first. Due to the buffering mechanism of Pascal, this has not
the same functionality as the \seem{dup2}{2} call in C. The internal Pascal
buffers are not the same after this call, but when the buffers are flushed
(e.g. after output), the output is sent to the same file.
Doing an lseek will, however, work as in C, i.e. doing a lseek will change the
fileposition in both files.

The function returns \var{True} if succesful, false otherwise.
\Errors
In case of error, \var{Linuxerror} is used to report errors.
\begin{description}
\item[sys\_ebadf] \var{OldFile} hasn't been assigned.
\item[sys\_emfile] Maximum number of open files for the process is reached.
\end{description}
\SeeAlso
 \seef{Dup}, \seem{Dup2}{2} 
\end{function}


\FPCexample{ex32}


\begin{procedure}{EpochToLocal}
\Declaration
Procedure EpochToLocal (Epoch : Longint; var Year,Month,Day,Hour,Minute,Second : Word);
\Description
Converts the epoch time (=Number of seconds since 00:00:00 , January 1,
1970, corrected for your time zone ) to local date and time.

This function takes into account the timzeone settings of your system.
\Errors
None
\SeeAlso
\seef{GetEpochTime}, \seef{LocalToEpoch}, \seep{GetTime},\seep{GetDate} 
\end{procedure}

\FPCexample{ex3}

\begin{procedure}{Execl}
\Declaration
Procedure Execl (Path : pathstr);
\Description
Replaces the currently running program with the program, specified in
\var{path}. Path is split into a command and it's options.
The executable in \var{path} is NOT searched in the path.
The current environment is passed to the program.
On success, \var{execl} does not return.

\Errors
Errors are reported in \var{LinuxError}:
\begin{description}
\item[sys\_eacces] File is not a regular file, or has no execute permission.
A compononent of the path has no search permission.
\item[sys\_eperm] The file system is mounted \textit{noexec}.
\item[sys\_e2big] Argument list too big.
\item[sys\_enoexec] The magic number in the file is incorrect.
\item[sys\_enoent] The file does not exist.
\item[sys\_enomem] Not enough memory for kernel, or to split command line.
\item[sys\_enotdir] A component of the path is not a directory.
\item[sys\_eloop] The path contains a circular reference (via symlinks).
\end{description}
\SeeAlso
\seep{Execve}, \seep{Execv}, \seep{Execvp}, \seep{Execle},
 \seep{Execlp}, \seef {Fork}, \seem{execvp}{3} 
\end{procedure}

\FPCexample{ex10}

\begin{procedure}{Execle}
\Declaration
Procedure Execle (Path : pathstr, Ep : ppchar);
\Description
Replaces the currently running program with the program, specified in
\var{path}. Path is split into a command and it's options.
The executable in \var{path} is searched in the path, if it isn't
an absolute filename.
The environment in \var{ep} is passed to the program.
On success, \var{execle} does not return.

\Errors
Errors are reported in \var{LinuxError}:
\begin{description}
\item[sys\_eacces] File is not a regular file, or has no execute permission.
A compononent of the path has no search permission.
\item[sys\_eperm] The file system is mounted \textit{noexec}.
\item[sys\_e2big] Argument list too big.
\item[sys\_enoexec] The magic number in the file is incorrect.
\item[sys\_enoent] The file does not exist.
\item[sys\_enomem] Not enough memory for kernel, or to split command line.
\item[sys\_enotdir] A component of the path is not a directory.
\item[sys\_eloop] The path contains a circular reference (via symlinks).
\end{description}
\SeeAlso
\seep{Execve}, \seep{Execv}, \seep{Execvp},
\seep{Execl}, \seep{Execlp}, \seef {Fork}, \seem{execvp}{3} 
\end{procedure}

\FPCexample{ex11}

\begin{procedure}{Execlp}
\Declaration
Procedure Execlp (Path : pathstr);
\Description
Replaces the currently running program with the program, specified in
\var{path}. Path is split into a command and it's options.
The executable in \var{path} is searched in the path, if it isn't
an absolute filename.
The current environment is passed to the program.
On success, \var{execlp} does not return.

\Errors
Errors are reported in \var{LinuxError}:
\begin{description}
\item[sys\_eacces] File is not a regular file, or has no execute permission.
A compononent of the path has no search permission.
\item[sys\_eperm] The file system is mounted \textit{noexec}.
\item[sys\_e2big] Argument list too big.
\item[sys\_enoexec] The magic number in the file is incorrect.
\item[sys\_enoent] The file does not exist.
\item[sys\_enomem] Not enough memory for kernel, or to split command line.
\item[sys\_enotdir] A component of the path is not a directory.
\item[sys\_eloop] The path contains a circular reference (via symlinks).
\end{description}
\SeeAlso
\seep{Execve}, \seep{Execv}, \seep{Execvp}, \seep{Execle},
\seep{Execl}, \seef {Fork}, \seem{execvp}{3} 
\end{procedure}

\FPCexample{ex12}

\begin{procedure}{Execv}
\Declaration
Procedure Execv (Path : pathstr; args : ppchar);
\Description
Replaces the currently running program with the program, specified in
\var{path}.
It gives the program the options in \var{args}.
This is a pointer to an array of pointers to null-terminated
strings. The last pointer in this array should be nil.
The current environment is passed to the program.
On success, \var{execv} does not return.

\Errors
Errors are reported in \var{LinuxError}:
\begin{description}
\item[sys\_eacces] File is not a regular file, or has no execute permission.
A compononent of the path has no search permission.
\item[sys\_eperm] The file system is mounted \textit{noexec}.
\item[sys\_e2big] Argument list too big.
\item[sys\_enoexec] The magic number in the file is incorrect.
\item[sys\_enoent] The file does not exist.
\item[sys\_enomem] Not enough memory for kernel.
\item[sys\_enotdir] A component of the path is not a directory.
\item[sys\_eloop] The path contains a circular reference (via symlinks).
\end{description}
\SeeAlso
\seep{Execve}, \seep{Execvp}, \seep{Execle},
\seep{Execl}, \seep{Execlp}, \seef {Fork}, \seem{execv}{3} 
\end{procedure}

\FPCexample{ex8}


\begin{procedure}{Execve}
\Declaration
Procedure Execve(Path:pchar;args:ppchar;ep:ppchar);
Procedure Execve (Path : pathstr; args,ep : ppchar);
\Description
Replaces the currently running program with the program, specified in
\var{path}.
It gives the program the options in \var{args}, and the environment in
\var{ep}. They are pointers to an array of pointers to null-terminated
strings. The last pointer in this array should be nil.
On success, \var{execve} does not return.
\Errors
Errors are reported in \var{LinuxError}:
\begin{description}
\item[eacces] File is not a regular file, or has no execute permission.
A compononent of the path has no search permission.
\item[sys\_ eperm] The file system is mounted \textit{noexec}.
\item[sys\_ e2big] Argument list too big.
\item[sys\_ enoexec] The magic number in the file is incorrect.
\item[sys\_ enoent] The file does not exist.
\item[sys\_ enomem] Not enough memory for kernel.
\item[sys\_ enotdir] A component of the path is not a directory.
\item[sys\_ eloop] The path contains a circular reference (via symlinks).
\end{description}
\SeeAlso
\seep{Execve}, \seep{Execv}, \seep{Execvp} \seep{Execle},
\seep{Execl}, \seep{Execlp}, \seef {Fork}, \seem{execve}{2} 
\end{procedure}

\FPCexample{ex7}

\begin{procedure}{Execvp}
\Declaration
Procedure Execvp (Path : pathstr; args : ppchar);
\Description
Replaces the currently running program with the program, specified in
\var{path}. The executable in \var{path} is searched in the path, if it isn't
an absolute filename.
It gives the program the options in \var{args}. This is a pointer to an array of pointers to null-terminated
strings. The last pointer in this array should be nil.
The current environment is passed to the program.
On success, \var{execvp} does not return.

\Errors
Errors are reported in \var{LinuxError}:
\begin{description}
\item[sys\_eacces] File is not a regular file, or has no execute permission.
A compononent of the path has no search permission.
\item[sys\_eperm] The file system is mounted \textit{noexec}.
\item[sys\_e2big] Argument list too big.
\item[sys\_enoexec] The magic number in the file is incorrect.
\item[sys\_enoent] The file does not exist.
\item[sys\_enomem] Not enough memory for kernel.
\item[sys\_enotdir] A component of the path is not a directory.
\item[sys\_eloop] The path contains a circular reference (via symlinks).
\end{description}
\SeeAlso
\seep{Execve}, \seep{Execv}, \seep{Execle},
\seep{Execl}, \seep{Execlp}, \seef {Fork}, \seem{execvp}{3} 
\end{procedure}

\FPCexample{ex9}


\begin{procedurel}{FD\_ZERO}{FDZero}
\Declaration
Procedure FD\_ZERO (var fds:fdSet);
\Description
\var{FD\_ZERO} clears all the filedescriptors in the file descriptor 
set \var{fds}.
\Errors
None.
\SeeAlso
\seef{Select}, 
\seef{SelectText}, 
\seef{GetFS}, 
\seepl{FD\_Clr}{FDClr},
\seepl{FD\_Set}{FDSet}, 
\seefl{FD\_IsSet}{FDIsSet}

\end{procedurel}
For an example, see \seef{Select}.

\begin{procedurel}{FD\_Clr}{FDClr}
\Declaration
Procedure FD\_Clr (fd:longint;var fds:fdSet);
\Description
 \var{FD\_Clr} clears file descriptor \var{fd} in filedescriptor s
  et \var{fds}.
\Errors
None.
\SeeAlso
\seef{Select}, 
\seef{SelectText}, 
\seef{GetFS},
\seepl{FD\_ZERO}{FDZero}, 
\seepl{FD\_Set}{FDSet}, 
\seefl{FD\_IsSet}{FDIsSet}
\end{procedurel}

For an example, see \seef{Select}.

\begin{functionl}{FD\_IsSet}{FDIsSet}
\Declaration
Function FD\_IsSet (fd:longint;var fds:fdSet) : boolean;
\Description
\var{FD\_Set} Checks whether file descriptor \var{fd} in filedescriptor set \var{fds}
is set.
\Errors
None.
\SeeAlso
\seef{Select}, \seef{SelectText}, \seef{GetFS},
\seepl{FD\_ZERO}{FDZero}, 
\seepl{FD\_Clr}{FDClr},
\seepl{FD\_Set}{FDSet}
\end{functionl}

For an example, see \seef{Select}.

\begin{procedurel}{FD\_Set}{FDSet}
\Declaration
Procedure FD\_Set (fd:longint;var fds:fdSet);
\Description
\var{FD\_Set} sets file descriptor \var{fd} in filedescriptor set \var{fds}.
\Errors
None.
\SeeAlso
\seef{Select}, \seef{SelectText}, \seef{GetFS},\seepl{FD\_ZERO}{FDZero}, 
\seepl{FD\_Clr}{FDClr}, \seefl{FD\_IsSet}{FDIsSet}
\end{procedurel}

For an example, see \seef{Select}.

\begin{function}{fdClose}
\Declaration
Function fdClose (fd:longint) : boolean;
\Description
\var{fdClose} closes a file with file descriptor \var{Fd}. The function
returns \var{True} if the file was closed successfully, \var{False}
otherwise. 

\Errors
Errors are returned in LinuxError
\SeeAlso
\seef{fdOpen}, \seef{fdRead}, \seef{fdWrite},\seef{fdTruncate},
\seef{fdFlush}, seef{FdSeek}
\end{function}
For an example, see \seef{fdOpen}.

\begin{function}{fdFlush}
\Declaration
Function fdFlush (fd:Longint) : boolean;
\Description
\var{fdflush} flushes the Linux kernel file buffer, so the file is actually
written to disk. This is NOT the same as the internal buffer, maintained by
Free Pascal. 
The function returns \var{True} if the call was successful, \var{false} if
an error occurred.
\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{fdOpen}, \seef{fdClose}, \seef{fdRead},\seef{fdWrite},
\seef{fdTruncate}, \seef{fdSeek}
\end{function}
For an example, see \seef{fdRead}.

\begin{function}{fdOpen}
\Declaration
Function fdOpen(PathName:String;flags:longint):longint;
Function fdOpen(PathName:Pchar ;flags:longint):longint;
Function fdOpen(PathName:String;flags,mode:longint):longint; 
Function fdOpen(PathName:Pchar ;flags,mode:longint):longint;
\Description
\var{fdOpen} opens a file in \var{PathName} with flags \var{flags} 
One of the following:
\begin{description}
\item [Open\_RdOnly] File is opened Read-only.
\item [Open\_WrOnly] File is opened Write-only.
\item [Open\_RdWr] File is opened Read-Write.
\end{description}
The flags may be\var{OR}-ed with one of the following constants:
\begin{description}
\item [Open\_Accmode] File is opened
\item [Open\_Creat] File is created if it doesn't exist.
\item [Open\_Excl] If the file is opened with \var{Open\_Creat} and it 
already exists, the call wil fail.
\item [Open\_NoCtty] If the file is a terminal device, it will NOT become
the process' controlling terminal.
\item [Open\_Trunc] If the file exists, it will be truncated.
\item [Open\_Append] the file is opened in append mode. {\em Before each
write}, the file pointer is positioned at the end of the file.
\item [Open\_NonBlock] The file is opened in non-blocking mode. No operation
on the file descriptor will cause the calling process to wait till.
\item [Open\_NDelay] Idem as \var{Open\_NonBlock}
\item [Open\_Sync] The file is opened for synchronous IO. Any write
operation on the file will not return untill the data is physically written
to disk.
\item [Open\_NoFollow] if the file is a symbolic link, the open fails.
(\linux 2.1.126 and higher only)
\item [Open\_Directory] if the file is not a directory, the open fails.
(\linux 2.1.126 and higher only)
\end{description}
\var{PathName} can be of type \var{PChar} or \var{String}.
The optional \var{mode} argument specifies the permissions to set when opening
the file. This is modified by the umask setting. The real permissions are
\var{Mode and not umask}.
The return value of the function is the filedescriptor, or a negative 
value if there was an error.

\Errors
Errors are returned in LinuxError
\SeeAlso
\seef{fdClose}, \seef{fdRead}, \seef{fdWrite},\seef{fdTruncate},
\seef{fdFlush}, \seef{fdSeek}
\end{function}

\FPCexample{ex19}

\begin{function}{fdRead}
\Declaration
Function fdRead (fd:longint;var buf;size:longint) : longint;
\Description
 \var{fdRead} reads at most \var{size} bytes from the file descriptor
\var{fd}, and stores them in \var{buf}. 
The function returns the number of bytes actually read, or -1 if
an error occurred.
No checking on the length of \var{buf} is done.

\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{fdOpen}, \seef{fdClose}, \seef{fdWrite},\seef{fdTruncate},
\seef{fdFlush}, \seef{fdSeek}
\end{function}

\FPCexample{ex20}

\begin{function}{fdSeek}
\Declaration
Function fdSeek (fd,Pos,SeekType:longint) : longint;
\Description
\var{fdSeek} sets the current fileposition of file \var{fd} to
\var{Pos}, starting from \var{SeekType}, which can be one of the following:
\begin{description}
\item [Seek\_Set] \ \var{Pos} is the absolute position in the file.
\item [Seek\_Cur] \ \var{Pos} is relative to the current position.
\item [Seek\_end] \ \var{Pos} is relative to the end of the file.
\end{description}
The function returns the new fileposition, or -1 of an error occurred.

\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{fdOpen}, \seef{fdWrite}, \seef{fdClose},
\seef{fdRead},\seef{fdTruncate},
 \seef{fdFlush}
\end{function}
For an example, see \seef{fdOpen}.

\begin{function}{fdTruncate}
\Declaration
Function fdTruncate (fd,size:longint) : boolean;
\Description
\var{fdTruncate} sets the length of a file in \var{fd} on \var{size}
bytes, where \var{size} must be less than or equal to the current length of
the file in \var{fd}.
The function returns \var{True} if the call was successful, \var{false} if
an error occurred.
\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{fdOpen}, \seef{fdClose}, \seef{fdRead},\seef{fdWrite},\seef{fdFlush},
\seef{fdSeek}
\end{function}

\begin{function}{fdWrite}
\Declaration
Function fdWrite (fd:longint;var buf;size:longint) : longint;
\Description
\var{fdWrite} writes at most \var{size} bytes from \var{buf} to
file descriptor \var{fd}.
The function returns the number of bytes actually written, or -1 if an error
occurred.

\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{fdOpen}, \seef{fdClose}, \seef{fdRead},\seef{fdTruncate},
\seef{fdSeek}, \seef{fdFlush}
\end{function}

\begin{function}{FExpand}
\Declaration
Function FExpand (Const Path: Pathstr) : pathstr;
\Description
 Expands \var {Path} to a full path, starting from root,
eliminating directory references such as . and .. from the result.

\Errors
None
\SeeAlso
\seef{BaseName},\seef{DirName} 
\end{function}

\FPCexample{ex45}

\begin{function}{FLock}
\Declaration
Function  Flock (fd,mode : longint) : boolean;
Function  Flock (var T : text;mode : longint) : boolean;
Function  Flock (var F : File;mode : longint) : boolean;
\Description
\var{FLock} implements file locking. it sets or removes a lock on the file
\var{F}. F can be of type \var{Text} or \var{File}, or it can be a \linux
filedescriptor (a longint)
\var{Mode} can be one of the following constants :
\begin{description}
\item [LOCK\_SH] \ sets a shared lock.
\item [LOCK\_EX] \ sets an exclusive lock.
\item [LOCK\_UN] \ unlocks the file.
\item [LOCK\_NB] \ This can be OR-ed together with the other. 
If this is done the application doesn't block when locking.
\end{description}

The function returns \var{True} if successful, \var{False} otherwise.
\Errors
If an error occurs, it is reported in \var{LinuxError}.
\SeeAlso
\seef{Fcntl}, \seem{flock}{2}
\end{function}

\begin{function}{FNMatch}
\Declaration
Function FNMatch(const Pattern,Name:string):Boolean;
\Description
\var{FNMatch} returns \var{True} if the filename in \var{Name}
matches the wildcard pattern in \var{Pattern}, \var{False} otherwise.

\var{Pattern} can contain the wildcards \var{*} (match zero or more 
arbitrary characters) or \var{?} (match a single character).
\Errors
None.
\SeeAlso
\seef{FSearch}, \seef{FExpand}
\end{function}

\FPCexample{ex69}

\begin{function}{FSearch}
\Declaration
Function FSearch (Path : pathstr;DirList : string) : Pathstr;
\Description
 Searches in \var{DirList}, a colon separated list of directories,
for a file named \var{Path}. It then returns a path to the found file.
\Errors
An empty string if no such file was found.
\SeeAlso
\seef{BaseName}, \seef{DirName}, \seef{FExpand}, \seef{FNMatch}
\end{function}

\FPCexample{ex46}

\begin{procedurel}{FSplit}{LFsplit}
\Declaration
Procedure FSplit(const Path:PathStr; \\
Var Dir:DirStr;Var Name:NameStr;Var Ext:ExtStr);
\Description
\var{FSplit} splits a full file name into 3 parts : A \var{Path}, a
\var{Name} and an extension  (in \var{ext}). 
The extension is taken to be all letters after the last dot (.).
\Errors
None.
\SeeAlso
\seef{FSearch}
\end{procedurel}

\FPCexample{ex67}

\begin{function}{FSStat}
\Declaration
Function FSStat (Path : Pathstr; Var Info : statfs) : Boolean;
Function FSStat (Fd:longint;Var Info:stat) : Boolean;
\Description
 Return in \var{Info} information about the filesystem on which the file
\var{Path} resides, or on which the file with file descriptor \var{fd}
resides. 
Info is of type \var{statfs}. The function returns \var{True} if the call 
was succesfull, \var{False} if the call failed.
\Errors
 \var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_enotdir] A component of \var{Path} is not a directory.
\item[sys\_einval] Invalid character in \var{Path}.
\item[sys\_enoent] \var{Path} does not exist.
\item[sys\_eaccess] Search permission is denied for  component in
\var{Path}.
\item[sys\_eloop] A circular symbolic link was encountered in \var{Path}.
\item[sys\_eio] An error occurred while reading from the filesystem.
\end{description}

\SeeAlso
\seef{FStat}, \seef{LStat}, \seem{statfs}{2}
\end{function}

\FPCexample{ex30}


\begin{function}{FStat}
\Declaration
Function FStat(Path:Pathstr;Var Info:stat):Boolean;
Function FStat(Fd:longint;Var Info:stat):Boolean;  
Function FStat(var F:Text;Var Info:stat):Boolean;  
Function FStat(var F:File;Var Info:stat):Boolean;  
\Description
\var{FStat} gets information about the file specified in one of the
following:
\begin{description}
\item [Path] a file on the filesystem.
\item [Fd] a valid file descriptor.
\item [F] an opened text file or untyped file.
\end{description}
and stores it in  \var{Info}, which is of type \var{stat}.
The function returns \var{True} if the call was succesfull, 
\var{False} if the call failed.

\Errors
 \var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_enoent] \var{Path} does not exist.
\end{description}
\SeeAlso
\seef{FSStat}, \seef{LStat}, \seem{stat}{2}
\end{function}

\FPCexample{ex28}

\begin{function}{Fcntl}
\Declaration
Function  Fcntl(Fd:longint;Cmd:Integer):integer;
Function  Fcntl(var Fd:Text;Cmd:Integer):integer;   
\Description
Read a file's attributes. \var{Fd} is an assigned file, or a valid file
descriptor.
\var{Cmd} speciefies what to do, and is one of the following:
\begin{description}
\item[F\_GetFd] Read the close\_on\_exec flag. If the low-order bit is 0, then
the file will remain open across execve calls.
\item[F\_GetFl] Read the descriptor's flags.
\item[F\_GetOwn] Get the Process ID of the owner of a socket.
\end{description}

\Errors
\var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_ebadf] \var{Fd} has a bad file descriptor.
\end{description}

\SeeAlso
\seep{Fcntl}, \seem{Fcntl}{2} 
\end{function}

\begin{procedure}{Fcntl}
\Declaration
Procedure Fcntl (Fd :  text, Cmd : Integer; Arg : longint);
Procedure Fcntl (Fd:longint;Cmd:longint;Arg:Longint);
\Description
Read or Set a file's attributes. \var{Fd} is an assigned file or a
valid file descriptor.
\var{Cmd} speciefies what to do, and is one of the following:
\begin{description}
\item[F\_SetFd] Set the close\_on\_exec flag of \var{Fd}. (only the least
siginificant bit is used).
\item[F\_GetLk] Return the \var{flock} record that prevents this process from
obtaining the lock, or set the \var{l\_type} field of the lock of there is no
obstruction. Arg is a pointer to a flock record.
\item[F\_SetLk] Set the lock or clear it (depending on \var{l\_type} in the
\var{flock} structure). if the lock is held by another process, an error
occurs.
\item[F\_GetLkw] Same as for \textbf{F\_Setlk}, but wait until the lock is
released.
\item[F\_SetOwn] Set the Process or process group that owns a socket.
\end{description}

\Errors

\var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_ebadf] \var{Fd} has a bad file descriptor.
\item[sys\_eagain or sys\_eaccess] For \textbf{F\_SetLk}, if the lock is
held by another process.
\end{description}

\SeeAlso
\seef{Fcntl}, \seem{Fcntl}{2}, seef{FLock}
\end{procedure}

\begin{function}{Fork}
\Declaration
Function Fork  : Longint;
\Description
Fork creates a child process which is a copy of the parent process.
Fork returns the process ID in the parent process, and zero in the child's
process. (you can get the parent's PID with \seef{GetPPid}).

\Errors
On error, -1 is returned to the parent, and no child is created.
\begin{description}
\item [sys\_eagain] Not enough memory to create child process.
\end{description}
\SeeAlso
\seep{Execve}, \seef{Clone}, \seem{fork}{2}
\end{function}

\begin{function}{FRename}
\Declaration
Function  FReName (OldName,NewName : Pchar) : Boolean;
Function  FReName (OldName,NewName : String) : Boolean;
\Description
\var{FRename} renames the file \var{OldName} to \var{NewName}. \var{NewName}
can be in a different directory than \var{OldName}, but it cannot be on
another partition (device). Any existing file on the new location will be replaced.

If the operation fails, then the \var{OldName} file will be preserved. 

The function returns \var{True} on succes, \var{False} on failure.
\Errors
On error, errors are reported in \var{LinuxError}. Possible errors include:
\begin{description}
\item[sys\_eisdir] \var{NewName} exists and is a directory, but \var{OldName}
is not a directory.
\item[sys\_exdev] \var{NewName} and \var{OldName} are on different devices.
\item[sys\_enotempty or sys\_eexist] \var{NewName} is an existing, non-empty
directory. 
\item[sys\_ebusy] \var{OldName} or \var{NewName} is a directory and is in
use by another process.
\item[sys\_einval] \var{NewName} is part of \var{OldName}.
\item[sys\_emlink] \var{OldPath} or \var{NewPath} already have tha maximum
amount of links pointing to them.
\item[sys\_enotdir] part of \var{OldName} or \var{NewName} is not
directory.
\item[sys\_efault] For the \var{pchar} case: One of the pointers points to
an invalid address.
\item[sys\_eaccess] access is denied when attempting to move the file.
\item[sys\_enametoolong] Either \var{OldName} or \var{NewName} is too long.
\item[sys\_enoent] a directory component in \var{OldName} or \var{NewName}
didn't exist.
\item[sys\_enomem] not enough kernel memory.
\item[sys\_erofs] \var{NewName} or \var{OldName} is on a read-only file
system.
\item[sys\_eloop] too many symbolic links were encountered trying to expand
\var{OldName} or \var{NewName}
\item[sys\_enospc] the filesystem has no room for the new directory entry.
\end{description}
\SeeAlso
\seef{UnLink}
\end{function}


\begin{procedure}{GetDate}
\Declaration
Procedure GetDate  (Var Year, Month, Day : Word) ;
\Description
Returns the current date.
\Errors
None
\SeeAlso
\seef{GetEpochTime}, \seep{GetTime},  \seep{GetDateTime}, \seep{EpochToLocal} 
\end{procedure}

\FPCexample{ex6}

\begin{procedure}{GetDateTime}
\Declaration
Procedure GetDateTime(Var Year,Month,Day,hour,minute,second:Word);
\Description
Returns the current date and time. The time is corrected for the local time
zone. This procedure is equivalent to the \seep{GetDate} and \var{GetTime}
calls.
\Errors
None
\SeeAlso
\seef{GetEpochTime}, \seep{GetTime}, \seep{EpochToLocal}, \seep{GetDate} 
\end{procedure}

\FPCexample{ex60}

\begin{function}{GetDomainName}
\Declaration
Function GetDomainName  : String;
\Description
Get the domain name of the machine on which the process is running.
An empty string is returned if the domain is not set.

\Errors
None.
\SeeAlso
 \seef{GetHostName},seem{Getdomainname}{2} 
\end{function}

\FPCexample{ex39}

\begin{function}{GetEGid}
\Declaration
Function GetEGid  : Longint;
\Description
 Get the effective group ID of the currently running process.
\Errors
None.
\SeeAlso
\seef{GetGid}, \seem{getegid}{2} 
\end{function}

\FPCexample{ex18}

\begin{function}{GetEUid}
\Declaration
Function GetEUid  : Longint;
\Description
 Get the effective user ID of the currently running process.
\Errors
None.
\SeeAlso
\seef{GetEUid}, \seem{geteuid}{2} 
\end{function}

\FPCexample{ex17}

\begin{function}{GetEnv}
\Declaration
Function GetEnv (P : String) : PChar;
\Description
Returns the value of the environment variable in \var{P}. If the variable is
not defined, nil is returned. The value of the environment variable may be
the empty string.
A PChar is returned to accomodate for strings longer than 255 bytes,
\var{TERMCAP} and \var{LS\_COLORS}, for instance.

\Errors
None.
\SeeAlso
\seem{sh}{1}, \seem{csh}{1} 
\end{function}

\FPCexample{ex41}

\begin{function}{GetEpochTime}
\Declaration
Function GetEpochTime  : longint;
\Description
returns the number of seconds since 00:00:00 gmt, january 1, 1970.
it is adjusted to the local time zone, but not to DST.

\Errors
no errors
\SeeAlso
\seep{EpochToLocal}, \seep{GetTime}, \seem{time}{2}
\end{function}

\FPCexample{ex1}

\begin{function}{GetFS}
\Declaration
Function GetFS (Var F : Any File Type) : Longint;
\Description
\var{GetFS} returns the file selector that the kernel provided for your
file. In principle you don' need this file selector. Only for some calls
it is needed, such as the \seef{Select} call or so.
\Errors
In case the file was not opened, then -1 is returned.
\SeeAlso
\seef{Select}
\end{function}

\FPCexample{ex34}

\begin{function}{GetGid}
\Declaration
Function GetGid  : Longint;
\Description
 Get the real group ID of the currently running process.
\Errors
None.
\SeeAlso
\seef{GetEGid}, \seem{getgid}{2} 
\end{function}

\FPCexample{ex18}

\begin{function}{GetHostName}
\Declaration
Function GetHostName  : String;
\Description
Get the hostname of the machine on which the process is running.
An empty string is returned if hostname is not set.

\Errors
None.
\SeeAlso
 \seef{GetDomainName},seem{Gethostname}{2} 
\end{function}

\FPCexample{ex40}

\begin{procedure}{GetLocalTimezone}
\Declaration
procedure GetLocalTimezone(timer:longint;var leap\_correct,leap\_hit:longint);
procedure GetLocalTimezone(timer:longint);
\Description
\var{GetLocalTimeZone} returns the local timezone information. It also
initializes the \var{TZSeconds} variable, which is used to correct the epoch time
to local time. 

There should never be any need to call this function directly. It is called by the
initialization routines of the Linux unit.
\SeeAlso
\seef{GetTimezoneFile}, \seep{ReadTimezoneFile}
\end{procedure}

\begin{function}{GetPid}
\Declaration
Function GetPid  : Longint;
\Description
 Get the Process ID of the currently running process.
\Errors
None.
\SeeAlso
\seef{GetPPid}, \seem{getpid}{2}
\end{function}

\FPCexample{ex16}

\begin{function}{GetPPid}
\Declaration
Function GetPPid  : Longint;
\Description
 Get the Process ID of the parent process.
\Errors
None.
\SeeAlso
\seef{GetPid}, \seem{getppid}{2}
\end{function}

\FPCexample{ex16}

\begin{function}{GetPriority}
\Declaration
Function GetPriority (Which,Who : Integer) : Integer;
\Description
GetPriority returns the priority with which a process is running.
Which process(es) is determined by the \var{Which} and \var{Who} variables.
\var{Which} can be one of the pre-defined \var{Prio\_Process, Prio\_PGrp,
Prio\_User}, in which case \var{Who} is the process ID, Process group ID or
User ID, respectively.

\Errors

 Error checking must be done on LinuxError, since a priority can be negative.
 \begin{description}
 \item[sys\_esrch] No process found using \var{which} and \var{who}.
 \item[sys\_einval] \var{Which} was not one of \var{Prio\_Process, Prio\_Grp
or Prio\_User}.
 \end{description}
 
\SeeAlso
\seef{SetPriority}, \seep{Nice}, \seem{Getpriority}{2}
\end{function}
For an example, see \seep{Nice}.

\begin{procedure}{GetTime}
\Declaration
procedure GetTime(var hour,min,sec,msec,usec:word);
procedure GetTime(var hour,min,sec,sec100:word);
procedure GetTime(var hour,min,sec:word);
\Description
Returns the current time of the day, adjusted to local time.
Upon return, the parameters are filled with
\begin{description}
\item[hour] Hours since 00:00 today.
\item[min] minutes in current hour.
\item[sec] seconds in current minute.
\item[sec100] hundreds of seconds in current second.
\item[msec] milliseconds in current second.
\item[usec] microseconds in current second.
\end{description}
\Errors
None
\SeeAlso
\seef{GetEpochTime}, \seep{GetDate}, \seep{GetDateTime}, \seep{EpochToLocal} 
\end{procedure}

\FPCexample{ex5}

\begin{procedure}{GetTimeOfDay}
\Declaration
Procedure GetTimeOfDay(var tv:timeval);
\Description
\var{GetTimeOfDay} returns the number of seconds since 00:00, January 1 
1970, GMT in a \var{timeval} record. This time NOT corrected any way, 
not taking into account timezones, daylight savings time and so on.

It is simply a wrapper to the kernel system call. To get the local time,
\seep{GetTime}.
\Errors
None.
\SeeAlso
\seep{GetTime}, \seef{GetTimeOfDay}
\end{procedure}

\begin{function}{GetTimeOfDay}
\Declaration
Function GetTimeOfDay:longint;
\Description
\var{GetTimeOfDay} returns the number of seconds since 00:00, January 1
1970, GMT. This time NOT corrected any way, not taking into account
timezones, daylight savings time and so on.

It is simply a wrapper to the kernel system call. To get the local time,
\seep{GetTime}.
\Errors
None.
\SeeAlso
\seep{GetTimeOfDay}, \seep{GetTime}
\end{function}

\begin{function}{GetTimezoneFile}
\Declaration
function GetTimezoneFile:string;
\Description
\var{GetTimezoneFile} returns the location of the current timezone file.
The location of file is determined as follows:
\begin{enumerate}
\item If \file{/etc/timezone} exists, it is read, and the contents of this
file is returned. This should work on Debian systems.
\item If \file{/usr/lib/zoneinfo/localtime} exists, then it is returned.
(this file is a symlink to the timezone file on SuSE systems)
\item If \file{/etc/localtime} exists, then it is returned. 
(this file is a symlink to the timezone file on RedHat systems)
\end{enumerate}
\Errors
If no file was found, an empty string is returned.
\SeeAlso
\seep{ReadTimezoneFile}
\end{function}

\begin{function}{GetUid}
\Declaration
Function GetUid  : Longint;
\Description
 Get the real user ID of the currently running process.
\Errors
None.
\SeeAlso
\seef{GetEUid}, \seem{getuid}{2} 
\end{function}

\FPCexample{ex17}

\begin{function}{Glob}
\Declaration
Function Glob (Const Path : Pathstr) : PGlob;
\Description
Glob returns a pointer to a glob structure which contains all filenames which
exist and match the pattern in \var{Path}.
The pattern can contain wildcard characters, which have their
usual meaning.

\Errors
 Returns nil on error, and \var{LinuxError} is set.
\begin{description}
\item[sys\_enomem] No memory on heap for glob structure.
\item[others] As returned by the opendir call, and sys\_readdir.
\end{description}

\SeeAlso
\seep{GlobFree}, \seem{Glob}{3} 
\end{function}

\FPCexample{ex49}

\begin{procedure}{GlobFree}
\Declaration
Procedure GlobFree (Var P : Pglob);
\Description
Releases the memory, occupied by a pglob structure. \var{P} is set to nil.
\Errors
None
\SeeAlso
 \seef{Glob} 
\end{procedure}
For an example, see \seef{Glob}.

\begin{procedure}{IOCtl}
\Declaration
Procedure IOCtl (Handle,Ndx: Longint; Data: Pointer);
\Description
This is a general interface to the Unix/ \linux ioctl call.
It performs various operations on the filedescriptor \var{Handle}.
\var{Ndx} describes the operation to perform.
\var{Data} points to data needed for the \var{Ndx} function. 
The structure of this data is function-dependent, so we don't elaborate on
this here. 
For more information on this, see various manual pages under linux.

\Errors

Errors are reported in LinuxError. They are very dependent on the used
function, that's why we don't list them here

\SeeAlso
\seem{ioctl}{2}
\end{procedure}

\FPCexample{ex54}

\begin{function}{IOperm}
\Declaration
Function IOperm (From,Num : Cadinal; Value : Longint) : boolean;
\Description
\var{IOperm}
  sets permissions on \var{Num} ports starting with port \var{From} to 
  \var{Value}. The function returns \var{True} if the call was successfull,
  \var{False} otherwise.
{\em Remark:}
\begin{itemize}
\item This works ONLY as root.
\item Only the first \var{0x03ff} ports can be set.
\item When doing a \seef{Fork}, the permissions are reset. When doing a
\seep{Execve} they are kept.
\end{itemize}

\Errors
Errors are returned in \var{LinuxError}
\SeeAlso
\seem{ioperm}{2}
\end{function}

\begin{function}{IsATTY}
\Declaration
Function IsATTY (var f) : Boolean;
\Description
Check if the filehandle described by \var{f} is a terminal.
f can be of type
\begin{enumerate}
\item \var{longint} for file handles;
\item \var{Text} for \var{text} variables such as \var{input} etc.
\end{enumerate}
Returns \var{True} if \var{f} is a terminal, \var{False} otherwise.

\Errors
No errors are reported
\SeeAlso
\seep{IOCtl},\seef{TTYName}
\end{function}
\begin{functionl}{S\_ISBLK}{ISBLK}
\Declaration
Function S\_ISBLK (m:integer) : boolean;
\Description
 \var{S\_ISBLK} checks the file mode \var{m} to see whether the file is a
block device file. If so it returns \var{True}.

\Errors
\seef{FStat},
 \seefl{S\_ISLNK}{ISLNK}, 
 \seefl{S\_ISREG}{ISREG},
 \seefl{S\_ISDIR}{ISDIR},
 \seefl{S\_ISCHR}{ISCHR},
 \seefl{S\_ISFIFO}{ISFIFO},
 \seefl{S\_ISSOCK}{ISSOCK}

\SeeAlso
ISLNK.
\end{functionl}
\begin{functionl}{S\_ISCHR}{ISCHR}
\Declaration
Function S\_ISCHR (m:integer) : boolean;
\Description
 \var{S\_ISCHR} checks the file mode \var{m} to see whether the file is a
character device file. If so it returns \var{True}.

\Errors
\seef{FStat},
 \seefl{S\_ISLNK}{ISLNK}, 
 \seefl{S\_ISREG}{ISREG},
 \seefl{S\_ISDIR}{ISDIR},
 \seefl{S\_ISBLK}{ISBLK},
 \seefl{S\_ISFIFO}{ISFIFO},
 \seefl{S\_ISSOCK}{ISSOCK}

\SeeAlso
ISLNK.
\end{functionl}
\begin{functionl}{S\_ISDIR}{ISDIR}
\Declaration
Function S\_ISDIR (m:integer) : boolean;
\Description
 \var{S\_ISDIR} checks the file mode \var{m} to see whether the file is a
directory. If so it returns \var{True}

\Errors
\seef{FStat},
 \seefl{S\_ISLNK}{ISLNK}, 
 \seefl{S\_ISREG}{ISREG},
 \seefl{S\_ISCHR}{ISCHR},
 \seefl{S\_ISBLK}{ISBLK},
 \seefl{S\_ISFIFO}{ISFIFO},
 \seefl{S\_ISSOCK}{ISSOCK}

\SeeAlso
ISLNK.
\end{functionl}
\begin{functionl}{S\_ISFIFO}{ISFIFO}
\Declaration
Function S\_ISFIFO (m:integer) : boolean;
\Description
 \var{S\_ISFIFO} checks the file mode \var{m} to see whether the file is a
fifo (a named pipe). If so it returns \var{True}.

\Errors
\seef{FStat},
 \seefl{S\_ISLNK}{ISLNK}, 
 \seefl{S\_ISREG}{ISREG},
 \seefl{S\_ISDIR}{ISDIR},
 \seefl{S\_ISCHR}{ISCHR},
 \seefl{S\_ISBLK}{ISBLK},
 \seefl{S\_ISSOCK}{ISSOCK}

\SeeAlso
ISLNK.
\end{functionl}

\begin{functionl}{S\_ISLNK}{ISLNK}
\Declaration
Function S\_ISLNK (m:integer) : boolean;
\Description
 \var{S\_ISLNK} checks the file mode \var{m} to see whether the file is a
symbolic link. If so it returns \var{True}

\Errors
\seef{FStat},
 \seefl{S\_ISREG}{ISREG},
 \seefl{S\_ISDIR}{ISDIR},
 \seefl{S\_ISCHR}{ISCHR},
 \seefl{S\_ISBLK}{ISBLK},
 \seefl{S\_ISFIFO}{ISFIFO},
 \seefl{S\_ISSOCK}{ISSOCK}

\SeeAlso
\end{functionl}


\FPCexample{ex53}

\begin{functionl}{S\_ISREG}{ISREG}
\Declaration
Function S\_ISREG (m:integer) : boolean;
\Description
 \var{S\_ISREG} checks the file mode \var{m} to see whether the file is a
regular file. If so it returns \var{True}

\Errors
\seef{FStat},
 \seefl{S\_ISLNK}{ISLNK}, 
 \seefl{S\_ISDIR}{ISDIR},
 \seefl{S\_ISCHR}{ISCHR},
 \seefl{S\_ISBLK}{ISBLK},
 \seefl{S\_ISFIFO}{ISFIFO},
 \seefl{S\_ISSOCK}{ISSOCK}

\SeeAlso
ISLNK.
\end{functionl}
\begin{functionl}{S\_ISSOCK}{ISSOCK}
\Declaration
Function S\_ISSOCK (m:integer) : boolean;
\Description
 \var{S\_ISSOCK} checks the file mode \var{m} to see whether the file is a
socket. If so it returns \var{True}.

\Errors
\seef{FStat},
 \seefl{S\_ISLNK}{ISLNK}, 
 \seefl{S\_ISREG}{ISREG},
 \seefl{S\_ISDIR}{ISDIR},
 \seefl{S\_ISCHR}{ISCHR},
 \seefl{S\_ISBLK}{ISBLK},
 \seefl{S\_ISFIFO}{ISFIFO}

\SeeAlso
ISLNK.
\end{functionl}

\begin{function}{Kill}
\Declaration
Function Kill (Pid : Longint; Sig : Integer) : Integer;
\Description
 Send a signal \var{Sig} to a process or process group. If \var{Pid}>0 then
the signal is sent to \var{Pid}, if it equals -1, then the signal is sent to
all processes except process 1. If \var{Pid}<-1 then the signal is sent to
process group -Pid.
The return value is zero, except in case three, where the return value is the
number of processes to which the signal was sent.

\Errors
\var{LinuxError} is used to report errors:
\begin{description}
\item[sys\_einval] An invalid signal is sent.
\item[sys\_esrch] The \var{Pid} or process group don't exist.
\item[sys\_eperm] The effective userid of the current process doesn't math
the one of process \var{Pid}.
\end{description}

\SeeAlso
\seep{SigAction}, \seef{Signal}, \seem{Kill}{2} 
\end{function}

\begin{function}{LStat}
\Declaration
Function LStat (Path : Pathstr; Var Info : stat) : Boolean;
\Description
\var{LStat} gets information about the link specified in \var{Path}, and stores it in 
\var{Info}, which is of type \var{stat}. Contrary to \var{FStat}, it stores
information about the link, not about the file the link points to.
The function returns \var{True} if the call was succesfull, \var{False} if the call
failed.

\Errors
 \var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_enoent] \var{Path} does not exist.
\end{description}

\SeeAlso
\seef{FStat}, \seef{FSStat}, \seem{stat}{2}
\end{function}

\FPCexample{ex29}

\begin{function}{Link}
\Declaration
Function Link (OldPath,NewPath : pathstr) : Boolean;
\Description
\var{Link} makes \var{NewPath} point to the same file als \var{OldPath}. The two files
then have the same inode number. This is known as a 'hard' link.
The function returns \var{True} if the call was succesfull, \var{False} if the call
failed.

\Errors
 Errors are returned in \var{LinuxError}.
\begin{description}
\item[sys\_exdev] \var {OldPath} and \var {NewPath} are not on the same
filesystem.
\item[sys\_eperm] The filesystem containing oldpath and newpath doesn't
support linking files.
\item[sys\_eaccess] Write access for the directory containing \var{Newpath}
is disallowed, or one of the directories in \var{OldPath} or {NewPath} has no
search (=execute) permission.
\item[sys\_enoent] A directory entry in \var{OldPath} or \var{NewPath} does
not exist or is a symbolic link pointing to a non-existent directory.
\item[sys\_enotdir] A directory entry in \var{OldPath} or \var{NewPath} is
nor a directory.
\item[sys\_enomem] Insufficient kernel memory.
\item[sys\_erofs] The files are on a read-only filesystem.
\item[sys\_eexist] \var{NewPath} already exists.
\item[sys\_emlink] \var{OldPath} has reached maximal link count.
\item[sys\_eloop] \var{OldPath} or \var{NewPath} has a reference to a circular
symbolic link, i.e. a symbolic link, whose expansion points to itself.
\item[sys\_enospc] The device containing \var{NewPath} has no room for anothe
entry.
\item[sys\_eperm] \var{OldPath} points to . or .. of a directory.
\end{description}

\SeeAlso
\seef{SymLink}, \seef{UnLink}, \seem{Link}{2} 
\end{function}

\FPCexample{ex21}

\begin{function}{LocalToEpoch}
\Declaration
Function LocalToEpoch (Year,Month,Day,Hour,Minute,Second : Word) : longint;
\Description
Converts the Local time to epoch time (=Number of seconds since 00:00:00 , January 1,
1970 ).

\Errors
None
\SeeAlso
\seef{GetEpochTime}, \seep{EpochToLocal}, \seep{GetTime},\seep{GetDate} 
\end{function}

\FPCexample{ex4}

\begin{function}{MkFifo}
\Declaration
Function MkFifo (PathName: String; Mode : Longint) : Boolean;
\Description
\var{MkFifo} creates named a named pipe in the filesystem, with name
\var{PathName} and mode {Mode}. 

\Errors
 \var{LinuxError} is used to report errors:
\begin{description}
\item[sys\_emfile] Too many file descriptors for this process.
\item[sys\_enfile] The system file table is full.
\end{description}

\SeeAlso
\seep{POpen}, \seef{MkFifo}, \seem{mkfifo}{4}
\end{function}

\begin{function}{MMap}
\Declaration
Function MMap(const m:tmmapargs):longint;
\Description
\var{MMap} maps or unmaps files or devices into memory. The different fields
of the argument \var{m} determine what and how the \var{mmap} maps this:
\begin{description}
\item[address] Address where to mmap the device. This address is a hint, 
and may not be followed.
\item[size] Size (in bytes) of area to be mapped.
\item[prot] Protection of mapped memory. This is a OR-ed combination of the
following constants:
\begin{description}
\item[PROT\_EXEC] The memory can be executed.
\item[PROT\_READ] The memory can be read.
\item[PROT\_WRITE] The memory can be written.
\item[PROT\_NONE] The memory can not be accessed.
\end{description}
\item[flags] Contains some options for the mmap call. It is an OR-ed
combination of the following constants:
\begin{description}
\item[MAP\_FIXED] Do not map at another address than the given address. If the
address cannot be used, \var{MMap} will fail.
\item[MAP\_SHARED] Share this map with other processes that map this object.
\item[MAP\_PRIVATE] Create a private map with copy-on-write semantics.
\item[MAP\_ANONYMOUS] \var{fd} does not have to be a file descriptor.
\end{description}
One of the options \var{MAP\_SHARED} and \var{MAP\_PRIVATE} must be present,
but not both at the same time.
\item[fd] File descriptor from which to map.
\item[offset] Offset to be used in file descriptor fd.
\end{description}

The function returns a pointer to the mapped memory, or a -1 in case of en
error.
\Errors
On error, -1 is returned and LinuxError is set to the error code:
\begin{description}
\item[Sys\_EBADF] \var{fd} is not a valid file descriptor and 
\var{MAP\_ANONYMOUS} was not specified.
\item[Sys\_EACCES] \var{MAP\_PRIVATE} was specified, but fd is not open for 
reading. Or \var{MAP\_SHARED} was asked and \var{PROT\_WRITE} is  set, fd 
is not open for writing
\item[Sys\_EINVAL] One of the record fields \var{Start}, \var{length} or 
\var{offset} is invalid.
\item[Sys\_ETXTBUSY] \var{MAP\_DENYWRITE} was set but the object specified  
by fd is open for writing.
\item[Sys\_EAGAIN] \var{fd} is locked, or too much memory is locked.
\item[Sys\_ENOMEM] Not enough memory for this operation.
\end{description}
\SeeAlso
\seef{MUnMap}, \seem{mmap}{2}
\end{function}

\FPCexample{ex66}

\begin{function}{MUnMap}
\Declaration
function MUnMap (P : Pointer; Size : Longint) : Boolean;
\Description
\var{MUnMap} unmaps the memory block of size \var{Size}, pointed to by 
\var{P}, which was previously allocated with \seef{MMap}.

The function returns \var{True} if successful, \var{False} otherwise.
\Errors
In case of error the function returns \var{False} and \var{LinuxError}
is set to an error value. See \seef{MMap} for possible error values.
\SeeAlso
\seef{MMap}, \seem{munmap}{2}
\end{function}

For an example, see \seef{MMap}.

\begin{function}{NanoSleep}
\Declaration
Function NanoSleep(const req : timespec;var rem : timespec) : longint;
\Description
\var{NanoSleep} suspends the process till a time period as specified
in \var{req} has passed. Then the function returns. If the
call was interrupted (e.g. by some signal) then the function may
return earlier, and \var{rem} will contain the remaining time till the
end of the intended period. In this case the return value will be 
-1, and \var{LinuxError} will be set to \var{EINTR}

If the function returns without error, the return value is zero.
\Errors
If the call was interrupted, -1 is returned, and \var{LinuxError} is set
to \var{EINTR}. If invalid time values were specified, then -1 is returned
and \var{LinuxError} is set to \var{EINVAL}.
\SeeAlso
\seep{Pause}, \seef{Alarm}
\end{function}

\FPCexample{ex70}

\begin{procedure}{Nice}
\Declaration
Procedure Nice ( N : Integer);
\Description
\var{Nice} adds \var{-N} to the priority of the running process. The lower the
priority numerically, the less the process is favored.
Only the superuser can specify a negative \var{N}, i.e. increase the rate at
which the process is run.

\Errors
 Errors are returned in \var{LinuxError}
\begin{description}
\item [sys\_eperm] A non-superuser tried to specify a negative \var{N}, i.e.
do a priority increase.
\end{description}

\SeeAlso
\seef{GetPriority}, \seef{SetPriority}, \seem{Nice}{2}
\end{procedure}

\FPCexample{ex15}

\begin{function}{Octal}
\Declaration
Function Octal(l:longint):longint;
\Description
\var{Octal} will convert a number specified as an octal number to it's
decimal value.

This is useful for the \seef{Chmod} call, where permissions are specified
as octal numbers.
\Errors
No checking is performed whether the given number is a correct Octal number.
e.g. specifying \var{998} is possible; the result will be wrong in that
case.
\SeeAlso
\seef{Chmod}.
\end{function}

\FPCexample{ex68}

\begin{function}{OpenDir}
\Declaration
Function OpenDir (f:pchar) : pdir;
Function OpenDir (f:string) : pdir;
\Description
 \var{OpenDir} opens the directory  \var{f}, and returns a \var{pdir}
pointer to a \var{Dir} record, which can be used to read the directory 
structure. If the directory cannot be opened, \var{nil} is returned.
\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{CloseDir}, \seef{ReadDir}, \seep{SeekDir}, \seef{TellDir},
\seem{opendir}{3}
\end{function}


\FPCexample{ex35}


\begin{procedure}{pause}
\Declaration
Procedure Pause;
\Description
\var{Pause} puts the process to sleep and waits until the application 
receives  a signal. If a signal handler is installed for the received 
sigal, the handler will be called and after that pause will return 
control to the process.
\Errors
None.
\end{procedure}

For an example, see \seef{Alarm}.


\begin{function}{PClose}
\Declaration
Function PClose (Var F : FileType) : longint;
\Description
 \var{PClose} closes a file opened with \var{POpen}. It waits for the
command to complete, and then returns the exit status of the command. 

\Errors
\var{LinuxError} is used to report errors. If it is different from zero,
the exit status is not valid.
\SeeAlso
\seep{POpen}
\end{function}
For an example, see \seep{POpen}

\begin{procedure}{POpen}
\Declaration
Procedure POpen (Var F : FileType; Cmd : pathstr; rw : char);
\Description
 Popen runs the command specified in \var{Cmd},
 and redirects the standard in or output of the
command to the other end of the pipe \var{F}. The parameter \var{rw}
indicates the direction of the pipe. If it is set to \var{'W'}, then F can
be used to write data, which will then be read by the command from stdinput.
If it is set to \var{'R'}, then the standard output of the command can be 
read from \var{F}. \var{F} should be reset or rewritten prior to using it.
\var{F} can be of type \var{Text} or \var{File}.
A file opened with \var {POpen} can be closed with \var{Close}, but also
with \seef{PClose}. The result is the same, but \var{PClose} returns the
exit status of the command \var{Cmd}.
\Errors
Errors are reported in \var{LinuxError} and are essentially those of the
Execve, Dup and AssignPipe commands.

\SeeAlso
\seef{AssignPipe}, \seem{popen}{3}, \seef{PClose}
\end{procedure}

\FPCexample{ex37}

\begin{function}{ReadDir}
\Declaration
Function ReadDir (p:pdir) : pdirent;
\Description
\var{ReadDir} reads the next entry in the directory pointed to by \var{p}.
It returns a \var{pdirent} pointer to a structure describing the entry.
If the next entry can't be read, \var{Nil} is returned.

\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{CloseDir}, \seef{OpenDir}, \seep{SeekDir}, \seef{TellDir},
\seem{readdir}{3}
\end{function}

For an example, see \seef{OpenDir}.

\begin{function}{ReadLink}
\Declaration
Function  ReadLink(name,linkname:pchar;maxlen:longint):longint;
Function  ReadLink(name:pathstr):pathstr;
\Description
\var{ReadLink} returns the file the symbolic link \var{name} is pointing 
to. The first form of this function accepts a buffer \var{linkname} of
length \var{maxlen} where the filename will be stored. It returns the
actual number of characters stored in the buffer.

The second form of the function returns simply the name of the file.
\Errors
On error, the first form of the function returns -1; the second one returns
an empty string. \var{LinuxError} is set to report errors:
\begin{description}
\item[SYS\_ENOTDIR] A part of the path in \var{Name} is not a directory.
\item[SYS\_EINVAL] maxlen is not positive, or the  file is not a symbolic link.
\item[SYS\_ENAMETOOLONG] A pathname, or a component of a pathname,  was  too
long.
\item[SYS\_ENOENT] the link \var{name} does not exist.
\item[SYS\_EACCES] No permission to search a directory in the path
\item[SYS\_ELOOP]  Too many symbolic links were encountered in  trans­
             lating the pathname.
\item[SYS\_EIO] An  I/O  error occurred while reading from the file
              system.
\item[SYS\_EFAULT] The buffer is not part of the the process's memory space.
\item[SYS\_ENOMEM] Not enough kernel memory was available.
\end{description}
\SeeAlso
\seef{SymLink}
\end{function}

\FPCexample{ex62}

\begin{procedure}{ReadPort}
\Declaration
Procedure ReadPort (Port : Longint; Var Value : Byte);
Procedure ReadPort (Port : Longint; Var Value : Word);
Procedure ReadPort (Port : Longint; Var Value : Longint);
\Description
\var{ReadPort} reads one Byte, Word or Longint from port \var{Port} into
\var{Value}.

Note that you need permission to read a port. This permission can be set by 
the root user with the \seef{IOperm} call.
\Errors
In case of an error (not enough permissions read this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso

\seef{IOperm}, \seep{ReadPortB}, \seep{ReadPortW}, \seep{ReadPortL},\seep{WritePort},
\seep{WritePortB}, \seep{WritePortL}, \seep{WritePortW}
\end{procedure}

\begin{procedure}{ReadPortB}
\Declaration
Procedure ReadPortB (Port : Longint; Var Buf; Count: longint);
Function  ReadPortB (Port : Longint): Byte;
\Description
The procedural form of \var{ReadPortB} reads \var{Count} bytes from port
\var{Port} and stores them in \var{Buf}. There must be enough memory
allocated at \var{Buf} to store \var{Count} bytes.

The functional form of \var{ReadPortB} reads 1 byte from port \var{B}
and returns the byte that was read.

Note that you need permission to read a port. This permission can be set by 
the root user with the \seef{IOperm} call.

\Errors
In case of an error (not enough permissions read this port), runtime 216 
({\em Access Violation}) will occur.

\SeeAlso
\seef{IOperm}, \seep{ReadPort}, \seep{ReadPortW}, \seep{ReadPortL},\seep{WritePort},
\seep{WritePortB}, \seep{WritePortL}, \seep{WritePortW}
\end{procedure}

\begin{procedure}{ReadPortL}
\Declaration
function  ReadPortL (Port : Longint): LongInt;
Procedure ReadPortL (Port : Longint; Var Buf; Count: longint);
\Description
The procedural form of \var{ReadPortL} reads \var{Count} longints from port
\var{Port} and stores them in \var{Buf}. There must be enough memory
allocated at \var{Buf} to store \var{Count} Longints.

The functional form of \var{ReadPortB} reads 1 longint from port \var{B}
and returns the longint that was read.

Note that you need permission to read a port. This permission can be set by 
the root user with the \seef{IOperm} call.
\Errors
In case of an error (not enough permissions read this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso
\seef{IOperm}, \seep{ReadPort}, \seep{ReadPortW}, \seep{ReadPortB},\seep{WritePort},
\seep{WritePortB}, \seep{WritePortL}, \seep{WritePortW}
\end{procedure}

\begin{procedure}{ReadPortW}
\Declaration
Procedure ReadPortW (Port : Longint; Var Buf; Count: longint);
function  ReadPortW (Port : Longint): Word;
\Description
The procedural form of \var{ReadPortB} reads \var{Count} words from port
\var{Port} and stores them in \var{Buf}. There must be enough memory
allocated at \var{Buf} to store \var{Count} words.

The functional form of \var{ReadPortB} reads 1 word from port \var{B}
and returns the word that was read.

Note that you need permission to read a port. This permission can be set by 
the root user with the \seef{IOperm} call.
\Errors
In case of an error (not enough permissions read this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso
\seef{IOperm}, \seep{ReadPort}, \seep{ReadPortB}, \seep{ReadPortL},\seep{WritePort},
\seep{WritePortB}, \seep{WritePortL}, \seep{WritePortW}
\end{procedure}


\begin{procedure}{ReadTimezoneFile}
\Declaration
procedure ReadTimezoneFile(fn:string);
\Description
\var{ReadTimeZoneFile} reads the timezone file \var{fn} and initializes
the local time routines based on the information found there.

There should be no need to call this function. The initialization routines
of the \file{linux} unit call this routine at unit startup.
\Errors 
None.
\SeeAlso
\seef{GetTimezoneFile}, \seep{GetLocalTimezone}
\end{procedure}


\begin{procedure}{SeekDir}
\Declaration
Procedure SeekDir (p:pdir;off:longint);
\Description
 \var{SeekDir} sets the directory pointer to the \var{off}-th entry in the
directory structure pointed to by \var{p}.
\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{CloseDir}, \seef{ReadDir}, \seef{OpenDir}, \seef{TellDir},
\seem{seekdir}{3}
\end{procedure}
For an example, see \seef{OpenDir}.

\begin{function}{Select}
\Declaration
Function Select (N : Longint; \\ var readfds,writefds,exceptfds : PFDset;
Var Timeout) : Longint;
\Description
\var{Select} checks one of the file descriptors in the \var{FDSets} to see if its
status changed.
\var{readfds, writefds} and \var{exceptfds} are pointers to arrays of 256
bits. If you want a file descriptor to be checked, you set the
corresponding element in the array to 1. The other elements in the array
must be set to zero. Three arrays are passed : The entries in \var{readfds}
are checked to see if characters become available for reading. The entries
in \var{writefds} are checked to see if it is OK to write to them, while
entries in \var{exceptfds} are cheked to see if an exception occorred on
them.
You can use the functions \seepl{FD\_ZERO}{FDZero}, \seepl{FD\_Clr}{FDClr}, 
\seepl{FD\_Set}{FDSet}, \seefl{FD\_IsSet}{FDIsSet} to manipulate the individual elements of a set.
The pointers can be nil.
\var{N} is the largest index of a nonzero entry plus 1. (= the largest
file-descriptor + 1).
\var{TimeOut} can be used to set a time limit. 
If \var{TimeOut} can be two types :
\begin{enumerate}
\item \var{TimeOut} is of type \var{PTime} and contains a
zero time, the call returns immediately. If \var{TimeOut} is \var{Nil}, the
kernel will wait forever, or until a status changed.    
\item \var{TimeOut} is of type \var{Longint}. If it is -1, this has the same
effect as a \var{Timeout} of type  \var{PTime} which is \var{Nil}.
Otherwise, \var{TimeOut} contains a time in milliseconds.
\end{enumerate}
 
When the TimeOut is reached, or one of the file descriptors has changed,
the \var{Select} call returns. On return, it will have modified the entries
in the array which have actually changed, and it returns the number of
entries that have been changed. If the timout was reached, and no decsriptor
changed, zero is returned; The arrays of indexes are undefined after that.
On error, -1 is returned.
\Errors
On error, the function returns -1, and Errors are reported in LinuxError :
\begin{description}
\item[SYS\_EBADF\ ] An invalid descriptot was specified in one of the sets.
\item[SYS\_EINTR\ ] A non blocked signal was caught.
\item[SYS\_EINVAL\ ]  \var{N} is negative or too big.
\item[SYS\_ENOMEM\ ] \var{Select} was unable to allocate memory for its 
 internal tables.
\end{description}
\SeeAlso
\seef{SelectText}, \seef{GetFS}, 
\seepl{FD\_ZERO}{FDZero},
\seepl{FD\_Clr}{FDClr},
\seepl{FD\_Set}{FDSet}, 
\seefl{FD\_IsSet}{FDIsSet}
\end{function}

\FPCexample{ex33}

\begin{function}{SelectText}
\Declaration
Function SelectText ( var T : Text; TimeOut :PTime) : Longint;
\Description
\var{SelectText} executes the \seef{Select} call on a file of type
\var{Text}. You can specify a timeout in \var{TimeOut}. The SelectText call
determines itself whether it should check for read or write, depending on
how the file was opened : With \var{Reset} it is checked for reading, with
\var{Rewrite} and \var{Append} it is checked for writing.
\Errors
See \seef{Select}. \var{SYS\_EBADF} can also mean that the file wasn't
opened.
\SeeAlso
\seef{Select}, \seef{GetFS}
\end{function}

\begin{function}{SetPriority}
\Declaration
Function SetPriority (Which,Who,Prio : Integer) : Integer;
\Description
SetPriority sets the priority with which a process is running.
Which process(es) is determined by the \var{Which} and \var{Who} variables.
\var{Which} can be one of the pre-defined \var{Prio\_Process, Prio\_PGrp,
Prio\_User}, in which case \var{Who} is the process ID, Process group ID or
User ID, respectively.
\var{Prio} is a value in the range -20 to 20.

\Errors

 Error checking must be done on LinuxError, since a priority can be negative.
 \begin{description}
 \item[sys\_esrch] No process found using \var{which} and \var{who}.
 \item[sys\_einval] \var{Which} was not one of \var{Prio\_Process, Prio\_Grp
or Prio\_User}.
 \item[sys\_eperm] A process was found, but neither its effective or real
 user ID match the effective user ID of the caller.
 \item [sys\_eacces] A non-superuser tried to a priority increase.
 \end{description}
 
\SeeAlso
\seef{GetPriority}, \seep{Nice}, \seem{Setpriority}{2}
\end{function}
For an example, see \seep{Nice}.

\begin{function}{Shell}
\Declaration
Function Shell (Command : String) : Longint;
\Description
\var{Shell} invokes the bash shell (\file{/bin/sh}), and feeds it the
command \var{Command} (using the \var{-c} option). The function then waits
for the command to complete, and then returns the exit
status of the command, or 127 if it could not complete the \seef{Fork} 
or \seep{Execve} calls.

\Errors
Errors are reported in LinuxError.
\SeeAlso
\seep{POpen}, \seef{Fork}, \seep{Execve}, \seem{system}{3}
\end{function}

\FPCexample{ex56}

\begin{procedure}{SigAction}
\Declaration
Procedure SigAction (Signum : Integer; Var Act,OldAct : PSigActionRec);
\Description
 Changes the action to take upon receipt of a signal. \var{Act} and
\var{Oldact} are pointers to a \var{SigActionRec} record.
\var{SigNum} specifies the signal, and can be any signal except
\textbf{SIGKILL} or \textbf{SIGSTOP}.
If \var{Act} is non-nil, then the new action for signal \var{SigNum} is taken
from it. If \var{OldAct} is non-nil, the old action is stored there.
\var{Sa\_Handler} may be \var{SIG\_DFL} for the default action or
\var{SIG\_IGN} to ignore the signal.
\var{Sa\_Mask} Specifies which signals should be ignord during the execution
of the signal handler.
\var{Sa\_Flags} Speciefies a series of flags which modify the behaviour of
the signal handler. You can 'or' none or more of the following :
\begin{description}
\item[SA\_NOCLDSTOP] If signum is \textbf{SIGCHLD} do not receive
notification when child processes stop.
\item[SA\_ONESHOT or SA\_RESETHAND] Restore the signal action to the default
state once the signal handler has been called.
\item[SA\_RESTART] For compatibility with BSD signals.
\item[SA\_NOMASK or SA\_NODEFER] Do not prevent the signal from being received
from within its own signal handler.
\end{description}

\Errors
\var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_einval] an invalid signal was specified, or it was
\textbf{SIGKILL} or \textbf{SIGSTOP}.
\item[sys\_efault] \var{Act,OldAct} point outside this process address space
\item[sys\_eintr] System call was interrupted.
\end{description}

\SeeAlso

\seep{SigProcMask}, \seef{SigPending}, \seep{SigSuspend}, \seef{Kill},
\seem{Sigaction}{2}

\end{procedure}

\FPCexample{ex57}

\begin{function}{SigPending}
\Declaration
Function SigPending  : SigSet;
\Description
Sigpending allows the examination of pending signals (which have been raised
while blocked.) The signal mask of pending signals is returned.

\Errors
None
\SeeAlso
\seep{SigAction}, \seep{SigProcMask}, \seep{SigSuspend}, \seef{Signal},
\seef{Kill}, \seem{Sigpending}{2} 
\end{function}

\begin{procedure}{SigProcMask}
\Declaration
Procedure SigProcMask (How : Integer; SSet,OldSSet : PSigSet);
\Description
Changes the list of currently blocked signals. The behaviour of the call
depends on \var{How} :
\begin{description}
\item[SIG\_BLOCK] The set of blocked signals is the union of the current set
and the \var{SSet} argument.
\item[SIG\_UNBLOCK] The signals in \var{SSet} are removed from the set of
currently blocked signals.
\item[SIG\_SETMASK] The list of blocked signals is set so \var{SSet}.
\end{description}
If \var{OldSSet} is non-nil, then the old set is stored in it.

\Errors
\var{LinuxError} is used to report errors.
\begin{description}
\item[sys\_efault] \var{SSet} or \var{OldSSet} point to an adress outside
the range of the process.
\item[sys\_eintr] System call was interrupted.
\end{description}

\SeeAlso
\seep{SigAction}, \seef{SigPending}, \seep{SigSuspend}, \seef{Kill},
\seem{Sigprocmask}{2} 
\end{procedure}

\begin{procedure}{SigRaise}
\Declaration
Procedure SigRaise(Sig:integer);
\Description
\var{SigRaise} sends a \var{Sig} signal to the current process.
\Errors
None.
\SeeAlso
\seef{Kill}, \seef{GetPid}
\end{procedure}

\FPCexample{ex65}

\begin{procedure}{SigSuspend}
\Declaration
Procedure SigSuspend (Mask : SigSet);
\Description
SigSuspend temporarily replaces the signal mask for the process with the one
given in \var{Mask}, and then suspends the process until a signal is received.

\Errors
None
\SeeAlso
\seep{SigAction}, \seep{SigProcMask}, \seef{SigPending}, \seef{Signal},
\seef{Kill}, \seem{SigSuspend}{2} 
\end{procedure}

\begin{function}{Signal}
\Declaration
Function Signal (SigNum : Integer; Handler : SignalHandler) : SignalHandler;
\Description
Signal installs a new signal handler for signal \var{SigNum}. This call has
the same functionality as the \textbf{SigAction} call.
The return value for Signal is the old signal handler, or nil on error.

\Errors
\var {LinuxError} is used to report errors :
\begin{description}
\item[SIG\_ERR] An error occurred.
\end{description}

\SeeAlso
\seep{SigAction},\seef{Kill}, \seem{Signal}{2} 
\end{function}

\FPCexample{ex58}

\begin{function}{StringToPPchar}
\Declaration
Function StringToPPChar(Var S:STring):ppchar;
\Description
\var{StringToPPChar} splits the string \var{S} in words, replacing any
whitespace with zero characters. It returns a pointer to an array of pchars
that point to the first letters of the words in S. This array is terminated
by a \var{Nil} pointer.

The function does {\em not} add a zero character to the end of the string
unless it ends on whitespace.

The function reserves memory on the heap to store the array of \var{PChar};
The caller is responsible for freeing this memory. 

This function can be called to create arguments for the various \var{Exec}
calls.
\Errors
None.
\SeeAlso
\seef{CreateShellArgV}, \seep{Execve}, \seep{Execv}
\end{function}

\FPCexample{ex70}

\begin{function}{SymLink}
\Declaration
Function SymLink (OldPath,NewPath : pathstr) : Boolean;
\Description
\var{SymLink} makes \var{Newpath} point to the file in \var{OldPath}, which doesn't
necessarily exist. The two files DO NOT have the same inode number.
This is known as a 'soft' link.
The permissions of the link are irrelevant, as they are not used when
following the link. Ownership of the file is only checked in case of removal
or renaming of the link.
The function returns \var{True} if the call was succesfull, \var{False} if the call
failed.

\Errors
 Errors are returned in \var{LinuxError}.
\begin{description}
\item[sys\_eperm] The filesystem containing oldpath and newpath doesn't
support linking files.
\item[sys\_eaccess] Write access for the directory containing \var{Newpath}
is disallowed, or one of the directories in \var{OldPath} or {NewPath} has no
search (=execute) permission.
\item[sys\_enoent] A directory entry in \var{OldPath} or \var{NewPath} does
not exist or is a symbolic link pointing to a non-existent directory.
\item[sys\_enotdir] A directory entry in \var{OldPath} or \var{NewPath} is
nor a directory.
\item[sys\_enomem] Insufficient kernel memory.
\item[sys\_erofs] The files are on a read-only filesystem.
\item[sys\_eexist] \var{NewPath} already exists.
\item[sys\_eloop] \var{OldPath} or \var{NewPath} has a reference to a circular
symbolic link, i.e. a symbolic link, whose expansion points to itself.
\item[sys\_enospc] The device containing \var{NewPath} has no room for anothe
entry.
\end{description}
\SeeAlso
\seef{Link}, \seef{UnLink}, \seef{ReadLink}, \seem{Symlink}{2} 
\end{function}

\FPCexample{ex22}

\begin{function}{SysInfo}
\Declaration
Function  SysInfo(var Info:TSysinfo):Boolean;
\Description
\var{SysInfo} returns system information in \var{Info}. Returned information
in \var{Info} includes:
\begin{description}
\item[uptime] Number of seconds since boot.
\item[loads]  1, 5 and 15 minute load averages.
\item[totalram] total amount of main memory.
\item[freeram] amount of free memory.
\item[sharedram] amount of shared memory
\item[bufferram] amount of memory used by buffers.
\item[totalswap] total amount of swapspace.
\item[freeswap] amount of free swapspace.
\item[procs] number of current processes.
\end{description}
\Errors
None.
\SeeAlso
\seep{Uname}
\end{function}

\FPCexample{ex64}

\begin{function}{TCDrain}
\Declaration
Function TCDrain (Fd:longint) : Boolean;
\Description
 \var{TCDrain}
  waits until all data to file descriptor \var{Fd} is transmitted.
  
  The function returns \var{True} if the call was succesfull, \var{False}
  otherwise.

\Errors
Errors are reported in LinuxError
\SeeAlso
\seem{termios}{2}
\end{function}

\begin{function}{TCFlow}
\Declaration
Function TCFlow (Fd,Act:longint) : Boolean;
\Description
 \var{TCFlow}
  suspends/resumes transmission or reception of data to or from the file
descriptor \var{Fd}, depending
  on the action \var {Act}. This can be one of the following pre-defined
values: 
\begin{description}
\item [TCOOFF\ ] suspend reception/transmission,
\item [TCOON\ ] resume  reception/transmission,
\item [TCIOFF\ ] transmit a stop character to stop input from the terminal, 
\item [TCION\ ] transmit start to resume input from the terminal.
\end{description}
The function returns \var{True} if the call was succesfull, \var{False}
otherwise.

\Errors
Errors are reported in LinuxError.
\SeeAlso
\seem{termios}{2}
\end{function}

\begin{function}{TCFlush}
\Declaration
Function TCFlush (Fd,QSel:longint) : Boolean;
\Description
 \var{TCFlush}
  discards all data sent or received to/from file descriptor \var{fd}. 
 \var{QSel} indicates which queue
  should be discard. It can be one of the following pre-defined values :
\begin{description}
\item [TCIFLUSH\ ] input,
\item [TCOFLUSH\ ] output,
\item [TCIOFLUSH\ ] both input and output.
\end{description}
The function returns \var{True} if the call was succesfull, \var{False}
otherwise.

\Errors
Errors are reported in LinuxError.
\SeeAlso
\seem{termios}{2}
\end{function}

\begin{function}{TCGetAttr}
\Declaration
Function TCGetAttr (fd:longint;var tios:TermIOS) : Boolean;
\Description
 \var{TCGetAttr}
  gets the terminal parameters from the terminal referred to by the file
  descriptor \var{fd} and returns them in a \var{TermIOS} structure \var{tios}. 
The function returns \var{True} if the call was succesfull, \var{False}
otherwise.

\Errors
Errors are reported in LinuxError
\SeeAlso
\seef{TCSetAttr}, \seem{termios}{2} 
\end{function}

\FPCexample{ex55}

\begin{function}{TCGetPGrp}
\Declaration
Function TCGetPGrp (Fd:longint;var Id:longint) : boolean;
\Description
 \var{TCGetPGrp}
  returns the process group ID of a foreground process group in \var{Id} 
  The function returns \var{True} if the call was succesfull, \var{False}
  otherwise

\Errors
Errors are reported in LinuxError
\SeeAlso
\seem{termios}{2}
\end{function}

\begin{function}{TCSendBreak}
\Declaration
Function TCSendBreak (Fd,Duration:longint) : Boolean;
\Description
 \var{TCSendBreak} 
  Sends zero-valued bits on an asynchrone serial connection decsribed by
  file-descriptor \var{Fd}, for duration \var{Duration}.
  The function returns \var{True} if the action was performed successfully,
\var{False} otherwise.

\Errors
Errors are reported in LinuxError.
\SeeAlso
\seem{termios}{2}
\end{function}

\begin{function}{TCSetAttr}
\Declaration
Function TCSetAttr (Fd:longint;OptAct:longint;var Tios:TermIOS) : Boolean;
\Description
 \var{TCSetAttr}
  Sets the terminal parameters you specify in a \var{TermIOS} structure
\var{Tios} for the terminal
  referred to by the file descriptor \var{Fd}. \var{OptAct} specifies an 
  optional action when the set need to be done,
  this could be one of the following pre-defined values:
 \begin{description}
\item [TCSANOW\ ] set immediately.
\item [TCSADRAIN\ ] wait for output.
\item [TCSAFLUSH\ ] wait for output and discard all input not yet read. 
\end{description}
The function Returns \var{True} if the call was succesfull, \var{False} 
otherwise.

\Errors
Errors are reported in LinuxError.
\SeeAlso
\seef{TCGetAttr}, \seem{termios}{2}
\end{function}
For an example, see \seef{TCGetAttr}.

\begin{function}{TCSetPGrp}
\Declaration
Function TCSetPGrp (Fd,Id:longint) : boolean;
\Description
 \var{TCSetPGrp} Sets the Process Group Id to \var{Id}. 
The function returns \var{True} if the call was successful, \var{False}
otherwise.

\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{TCGetPGrp}, \seem{termios}{2}
\end{function}
For an example, see \seef{TCGetPGrp}.

\begin{function}{TTYName}
\Declaration
Function TTYName (var f) : String;
\Description
Returns the name of the terminal pointed to by \var{f}. \var{f}
must be a terminal. \var{f} can be of type:
\begin{enumerate}
\item \var{longint} for file handles;
\item \var{Text} for \var{text} variables such as \var{input} etc.
\end{enumerate}

\Errors
 Returns an empty string in case of an error. \var{Linuxerror} may be set
 to indicate what error occurred, but this is uncertain.
\SeeAlso
\seef{IsATTY},\seep{IOCtl}
\end{function}

\begin{function}{TellDir}
\Declaration
Function TellDir (p:pdir) : longint;
\Description
 \var{TellDir} returns the current location in the directory structure
pointed to by \var{p}. It returns -1 on failure.
\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{CloseDir}, \seef{ReadDir}, \seep{SeekDir}, \seef{OpenDir},
\seem{telldir}{3}
\end{function}
For an example, see \seef{OpenDir}.

\begin{function}{Umask}
\Declaration
Function Umask (Mask : Integer) : Integer;
\Description
Change the file creation mask for the current user to \var{Mask}. The
current mask is returned.

\Errors
None
\SeeAlso
\seef{Chmod}, \seem{Umask}{2}
\end{function}

\FPCexample{ex27}

\begin{procedure}{Uname}
\Declaration
Procedure Uname (var unamerec:utsname);
\Description
\var{Uname} gets the name and configuration of the current \linux kernel,
and returns it in \var{unamerec}.

\Errors
\var{LinuxError} is used to report errors.
\SeeAlso
\seef{GetHostName}, \seef{GetDomainName}, \seem{uname}{2}
\end{procedure}

\begin{function}{UnLink}
\Declaration
Function UnLink (Var Path) : Boolean;
\Description
\var{UnLink} decreases the link count on file \var{Path}. \var{Path} can be
of type \var{PathStr} or \var{PChar}. If the link count is zero, the
file is removed from the disk.
The function returns \var{True} if the call was succesfull, \var{False} if the call
failed.

\Errors
 Errors are returned in \var{LinuxError}.
\begin{description}
\item[sys\_eaccess] You have no write access right in the directory
containing \var{Path}, or you have no search permission in one of the
directory components of \var{Path}.
\item[sys\_eperm] The  directory containing pathname has the sticky-bit 
set and the process's effective  uid is neither the uid of the 
file to be deleted nor that of the directory containing it.
\item[sys\_enoent] A component of the path doesn't exist.
\item[sys\_enotdir] A directory component of the path is not a directory.
\item[sys\_eisdir] \var{Path} refers to a directory.
\item[sys\_enomem] Insufficient kernel memory.
\item[sys\_erofs] \var{Path} is on a read-only filesystem. 
\end{description}

\SeeAlso
\seef{Link}, \seef{SymLink}, \seem{Unlink}{2} 
\end{function}
For an example, see \seef{Link}.

\begin{function}{Utime}
\Declaration
Function Utime (path : pathstr; utim : utimbuf) : Boolean;
\Description
\var{Utime} sets the access and modification times of a file.
the \var{utimbuf} record contains 2 fields, \var{actime}, and \var{modtime},
both of type Longint. They should be filled with an epoch-like time,
specifying, respectively, the last access time, and the last modification
time. 
For some filesystem (most notably, FAT), these times are the same. 

\Errors
Errors are returned in \var{LinuxError}.
\begin{description}
\item[sys\_eaccess] One of the directories in \var{Path} has no
search (=execute) permission.
\item[sys\_enoent] A directory entry in \var{Path} does
not exist or is a symbolic link pointing to a non-existent directory.
\end{description}
Other errors may occur, but aren't documented.

\SeeAlso
\seef{GetEpochTime}, \seef{Chown}, \seef{Access}, \seem{utime}(2)
\end{function}

\FPCexample{ex25}

\begin{function}{WaitPid}
\Declaration
Function WaitPid (Pid : longint; Status : pointer; Options : Longint) : Longint;
\Description
 \var{WaitPid} waits for a child process with process ID \var{Pid} to exit. The
value of \var{Pid} can be one of the following:
\begin{description}
\item[Pid < -1] Causes \var{WaitPid} to wait for  any  child  process  whose
              process group ID equals the absolute value of \var{pid}.
\item[Pid = -1] Causes \var{WaitPid} to wait for any child process.
\item[Pid = 0] Causes \var{WaitPid} to wait for  any  child  process  whose
              process  group  ID  equals the one of the calling
              process.
\item[Pid > 0] Causes \var{WaitPid} to wait for the child whose process  ID
equals the value of \var{Pid}.
\end{description}
The \var{Options} parameter can be used to specify further how \var{WaitPid}
behaves:
\begin{description}
\item [WNOHANG] Causes \var{Waitpid} to return immediately if no child  has
exited.
\item [WUNTRACED] Causes \var{WaitPid} to return also for children which are
stopped, but whose status has not yet been reported.
\item[\_\_WCLONE] Causes \var{WaitPid} also to wait for threads created by
the \seef{Clone} call.
\end{description} 
Upon return, it returns the exit status of the process, or -1 in case of
failure. 

\Errors
Errors are returned in LinuxError.
\SeeAlso
\seef{Fork}, \seep{Execve}, \seem{waitpid}{2}
\end{function}

For an example, see \seef{Fork}.

\begin{procedure}{WritePort}
\Declaration
Procedure WritePort (Port : Longint; Value : Byte);
Procedure WritePort (Port : Longint; Value : Word);
Procedure WritePort (Port : Longint; Value : Longint);
\Description
\var{WritePort} writes \var{Value} -- 1 byte, Word or longint -- 
to port \var{Port}.

Note: You need permission to write to a port. This permission can be set with root
permission with the \var{IOperm} call.
\Errors
In case of an error (not enough permissions to write to this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso
\seef{IOperm}, \seep{WritePortB}, \seep{WritePortL}, \seep{WritePortW},
\seep{ReadPortB}, \seep{ReadPortL}, \seep{ReadPortW}
\end{procedure}


\begin{procedure}{WritePortB}
\Declaration
Procedure WritePortB (Port : Longint; Value : Byte);
Procedure WritePortB (Port : Longint; Var Buf; Count: longint);
\Description
The first form of \var{WritePortB} writes 1 byte to port \var{Port}.
The second form writes \var{Count} bytes from \var{Buf} to port \var{Port}.

Note: You need permission to write to a port. This permission can be set with root
permission with the \var{IOperm} call.
\Errors
In case of an error (not enough permissions to write to this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso
\seef{IOperm}, \seep{WritePort}, \seep{WritePortL}, \seep{WritePortW},
\seep{ReadPortB}, \seep{ReadPortL}, \seep{ReadPortW}
\end{procedure}


\begin{procedure}{WritePortL}
\Declaration
Procedure WritePortL (Port : Longint; Value : Longint);
Procedure WritePortL (Port : Longint; Var Buf; Count: longint);
\Description
The first form of \var{WritePortB} writes 1 byte to port \var{Port}.
The second form writes \var{Count} bytes from \var{Buf} to port \var{Port}.

Note: You need permission to write to a port. This permission can be set with root
permission with the \var{IOperm} call.
\Errors
In case of an error (not enough permissions to write to this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso
\seef{IOperm}, \seep{WritePort}, \seep{WritePortB}, \seep{WritePortW},
\seep{ReadPortB}, \seep{ReadPortL}, \seep{ReadPortW}
\end{procedure}


\begin{procedure}{WritePortW}
\Declaration
Procedure WritePortW (Port : Longint; Var Buf; Count: longint);
Procedure WritePortW (Port : Longint; Value : Word);
\Description
The first form of \var{WritePortB} writes 1 byte to port \var{Port}.
The second form writes \var{Count} bytes from \var{Buf} to port \var{Port}.

Note: You need permission to write to a port. This permission can be set with root
permission with the \var{IOperm} call.
\Errors
In case of an error (not enough permissions to write to this port), runtime 216 
({\em Access Violation}) will occur.
\SeeAlso
\seef{IOperm}, \seep{WritePort}, \seep{WritePortL}, \seep{WritePortB},
\seep{ReadPortB}, \seep{ReadPortL}, \seep{ReadPortW}
\end{procedure}