Some System Calls, Etc

CS330 Introduction to Operating Systems

Some UNIX System Calls / Library Functions

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perror

fork

getpid

getppid

getuid

chmod

chdir

getcwd

execl

execlp

exit

_exit

sleep

kill

wait

waitpid

signal

creat

open

read

write

link

unlink

stat

pipe

dup

dup2

brk

sbrk

Include Files(s)	<stdio.h>		Manual Section	3c
Summary	void perror( const char *s);
Purpose	Print an error message based on the value of errno.
Return	Success	Failure	Sets errno

Include Files(s)	<sys/types.h> <unistd.h>		Manual Section	2
Summary	pid_t fork( void );
Purpose	Create a child process.
Return	Success	Failure	Sets errno
	0 in child, child PID in parent	-1	Yes

Include Files(s)	<sys/types.h> <unistd.h>		Manual Section	2
Summary	pid_t getpid( void );
Purpose	Determine the process identifier (pid) for the current process.
Return	Success	Failure	Sets errno
	The process ID	-1	Yes

Include Files(s)	<sys/types.h> <unistd.h>		Manual Section	2
Summary	pid_t getppid( void );
Purpose	Determine the process identifier of the parent process.
Return	Success	Failure	Sets errno
	The parent process ID	-1	Yes

Include Files(s)	<sys/types.h> <unistd.h>		Manual Section	2
Summary	uid_t getuid( void );
Purpose	Obtain the user’s identifier (uid).
Return	Success	Failure	Sets errno
	The requested identifier

Include Files(s)	<sys/types.h> <sys/stat.h>		Manual Section	2
Summary	int chmod( const char *path, mode_t mode );
Purpose	Change the access permissions of a file or directory.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	3c
Summary	int chdir(const char *path );
Purpose	Change the working directory of a process.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	extern char *getcwd( char *buf, size_t size );
Purpose	Get the current working directory of a process and place it in buf, which contains size bytes.
Return	Success	Failure	Sets errno
	A pointer to the current directory name	NULL	Yes

Include Files(s)	<sys/types.h> <unistd.h>		Manual Section	2
Summary	int execl( const char file_pathname, const char arg0, ... . . . const char argn, char /* NULL */ );
Purpose	Obtain code to execute from the executable file specified by a filename optionally preceded by a directory path.
Return	Success	Failure	Sets errno
	Does not return	-1	Yes

Include Files(s)	<sys/types.h> <unistd.h>		Manual Section	2
Summary	int execlp( const char file, const char arg0, ... . . . const char argn, char /* NULL */ );
Purpose	Obtain code to execute from the executable file specified by the filename, searching the directories given in the PATH environment variable.
Return	Success	Failure	Sets errno
	Does not return	-1	Yes

Include Files(s)	<stdlib.h>		Manual Section	3c
Summary	void exit( int status);
Purpose	Terminate the current process by executing the at exit functions, cleaning up standard input/output with _cleanup, and calling _exit to terminate the process.
Return	Success	Failure	Sets errno
	No return	No return

Include Files(s)	<unistd.h>		Manual Section	2
Summary	void _exit( void );
Purpose	Terminate the current process.
Return	Success	Failure	Sets errno
	Does not return	Does not return

Include Files(s)	<unistd.h>		Manual Section	3c
Summary	unsigned sleep( unsigned seconds );
Purpose	Suspend the current process for the specified number of seconds.
Return	Success	Failure	Sets errno
	Amount of unslept time remaining

Include Files(s)	<sys/types.h> <signal.h>		Manual Section	2
Summary	int kill( pid_t pid, int sig );
Purpose	Send a specified signal to a specified process.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<sys/types.h> <sys/wait.h>		Manual Section	2
Summary	pid_t wait( int *stat_loc );
Purpose	Wait for a signal; ordinarily this will be the signal from a terminating child process.
Return	Success	Failure	Sets errno
	Child PID	-1	Yes

Value stored at stat_loc:

Child terminated normally:

byte 3	byte 2	byte 1	byte 0
		exit code	0

Child terminated due to an uncaught signal:

byte 3	byte 2	byte 1	byte 0
		0	signal #

Include Files(s)	<sys/types.h> <sys/wait.h>		Manual Section	2
Summary	pid_t waitpid( pid_t pid, int *stat_loc, int options );
Purpose	Wait for a signal from a specified process or group of processes. Ordinarily this will be the signal from a terminating child.
Return	Success	Failure	Sets errno
	Child PID or 0	-1	Yes

Include Files(s)	<signal.h>		Manual Section	2
Summary	void *signal( int sig, void (*disp) (int))) (int);
Purpose	Set the entry in the signal handler table for a specified type of signal.
Return	Success	Failure	Sets errno
	Signal’s previous disposition	SIG_ERR (-1)	Yes

Include Files(s)	<sys/types.h> <sys/stat.h> <fcntl.h>		Manual Section	2
Summary	int creat ( const char *path, mode_t mode );
Purpose	Create a file and open it for writing. The link count of the new file is set to 1.
Return	Success	Failure	Sets errno
	Lowest available file descriptor.	-1	Yes

Include Files(s)	<sys/types.h> <sys/stat.h> <fcntl.h>		Manual Section	2
Summary	int open ( const char path, int flags, / mode_t mode */);
Purpose	Opens a file; sets the file status to oflags, and if the file is being created, sets the permission mode to mode.
Return	Success	Failure	Sets errno
	Lowest available file descriptor	-1	Yes

Some flags are O_RDONLY, O_WRONLY, O_RDWR, O_NDELAY, O_NONBLOCK,

O_APPEND, O_CREAT, O_BINARY

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int close ( int filedescr );
Purpose	Closes a file.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int read ( int filedescr, char *buf, int numbytes );
Purpose	Read (at most) the specified number of bytes from the file identified by the file descriptor and store them at the address given by buf.
Return	Success	Failure	Sets errno
	Number of characters read	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int write ( int filedescr, char *buf, int numbytes );
Purpose	Write (at most) the specified number of bytes to the file identified by the file descriptor, obtaining them starting at the address given by buf.
Return	Success	Failure	Sets errno
	Number of characters written	-1	Yes

Include Files(s)	<sys/types.h> <sys/stat.h> <fcntl.h>		Manual Section	2
Summary	int link ( const char path1, const char path2);
Purpose	Create a hard link from the existing file pointed to by path1 to the new name pointed to by path2. The link count of the existing file is increased by one.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int unlink ( const char *path );
Purpose	Reduce the link count by one for the file specified by path; if the link count reaches zero, remove the file.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<sys/types.h> <sys/stat.h>		Manual Section	2
Summary	int stat ( const char path, structu stat buf);
Purpose	Obtain file related information.
Return	Success	Failure	Sets errno
		-1	Yes

Fields of the stat structure
Type	Field name	Purpose
dev_t	st_dev	/* device that file resides on */
ino_t	st_ino	/* this file’s number */
u_short	st_mode	/* protection */
short	st_nlink;	/* number of hard links to the file */
short	st_uid;	/* user ID of owner */
short	st_gid;	/* group ID of owner */
dev_t	st_rdev;	/* the device identifier (special files only) */
off_t	st_size;	/* total size of file, in bytes */
time_t	st_atime;	/* file data last access time */
time_t	st_mtime;	/* file data last modify time */
time_t	st_ctime;	/* file data last status change time */
long	st_blksize;	/* preferred blocksize for file system I/O */
long	st_blocks;	/* actual number of blocks allocated */

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int pipe ( int filedescr[2]);
Purpose	Create an I/O mechanism called a pipe and sets filedescr[0] to the file descriptor for reading from this pipe and filedescr[1] to the file descriptor for writing to it.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int dup ( int filedescr);
Purpose	Duplicates a file descriptor in the next available position in the file descriptor table.
Return	Success	Failure	Sets errno
	file descriptor (nonnegative)	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int dup2 ( int filedescr1, int filedescr2);
Purpose	Causes filedescr2 to refer to the same open file (or pipe, etc.) as filedescr1.
Return	Success	Failure	Sets errno
	filedescr2	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int brk (void *endds);
Purpose	Sets the break value (address of the first location beyond the end of the data segment) to endds and changes the allocated space accordingly.
Return	Success	Failure	Sets errno
	0	-1	Yes

Include Files(s)	<unistd.h>		Manual Section	2
Summary	int sbrk (intptr_t incr);
Purpose	Adds incr function bytes to the break value and changes the allocated space accordingly. The incr function can be negative.
Return	Success	Failure	Sets errno
	previous break value	(void *)-1	Yes

Fields of the stat structure