Functions used to manage files. More...

Macros
#define	STDIN_FILENO 0
	Standard input file descriptor.

#define	STDOUT_FILENO 1
	Standard output file descriptor.

#define	STDERR_FILENO 2
	Standard error file descriptor.

#define	stdin STDIN_FILENO
	Standard input file descriptor.

#define	stdout STDOUT_FILENO
	Standard output file descriptor.

#define	stderr STDERR_FILENO
	Standard error file descriptor.

Functions
ssize_t	read (int fd, void *buf, size_t nbytes)
	Read data from a file descriptor. More...

ssize_t	write (int fd, const void *buf, size_t nbytes)
	Write data into a file descriptor. More...

int	open (const char *pathname, int flags, mode_t mode)
	Opens the file specified by pathname. More...

int	close (int fd)
	Close a file descriptor. More...

off_t	lseek (int fd, off_t offset, int whence)
	Repositions the file offset inside a file. More...

int	unlink (const char *path)
	Delete a name and possibly the file it refers to. More...

int	symlink (const char linkname, const char path)
	Creates a symbolic link. More...

int	readlink (const char path, char buffer, size_t bufsize)
	Read the symbolic link, if present. More...

void	exit (int status)
	Wrapper for exit system call. More...

pid_t	getpid (void)
	Returns the process ID (PID) of the calling process. More...

pid_t	getsid (pid_t pid)
	Return session id of the given process. If pid == 0 return the SID of the calling process If pid != 0 return the SID corresponding to the process having identifier == pid. More...

pid_t	setsid (void)
	creates a new session if the calling process is not a process group leader. The calling process is the leader of the new session (i.e., its session ID is made the same as its process ID). The calling process also becomes the process group leader of a new process group in the session (i.e., its process group ID is made the same as its process ID). More...

pid_t	getpgid (pid_t pid)
	returns the Process Group ID (PGID) of the process specified by pid. If pid is zero, the process ID of the calling process is used. More...

int	setpgid (pid_t pid, pid_t pgid)
	Sets the Process Group ID (PGID) of the process specified by pid. If pid is zero, the process ID of the calling process is used. More...

gid_t	getgid (void)
	returns the real group ID of the calling process. More...

gid_t	getegid (void)
	returns the effective group ID of the calling process. More...

int	setgid (gid_t gid)
	sets the group IDs of the calling process. More...

int	setregid (gid_t rgid, gid_t egid)
	sets the real and effective group IDs of the calling process. More...

uid_t	getuid (void)
	Returns the real User ID of the calling process. More...

uid_t	geteuid (void)
	Returns the effective User ID of the calling process. More...

int	setuid (uid_t uid)
	Sets the User IDs of the calling process. More...

int	setreuid (uid_t ruid, uid_t euid)
	Sets the effective and real User IDs of the calling process. More...

pid_t	getppid (void)
	Returns the parent process ID (PPID) of the calling process. More...

pid_t	fork (void)
	Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is replaced by a call to ‘execve’. More...

int	execl (const char path, const char arg,...)
	Replaces the current process image with a new process image (argument list). More...

int	execlp (const char file, const char arg,...)
	Replaces the current process image with a new process image (argument list). More...

int	execle (const char path, const char arg,...)
	Replaces the current process image with a new process image (argument list). More...

int	execlpe (const char file, const char arg,...)
	Replaces the current process image with a new process image (argument list). More...

int	execv (const char path, char const argv[])
	Replaces the current process image with a new process image (argument vector). More...

int	execvp (const char file, char const argv[])
	Replaces the current process image with a new process image (argument vector). More...

int	execve (const char path, char const argv[], char *const envp[])
	Replaces the current process image with a new process image (argument vector), allows the caller to specify the environment of the executed program via `envp`. More...

int	execvpe (const char file, char const argv[], char *const envp[])
	Replaces the current process image with a new process image (argument vector), allows the caller to specify the environment of the executed program via `envp`. More...

int	nice (int inc)
	Adds inc to the nice value for the calling thread. More...

int	reboot (int magic1, int magic2, unsigned int cmd, void *arg)
	Reboots the system, or enables/disables the reboot keystroke. More...

char *	getcwd (char *buf, size_t size)
	Get current working directory. More...

int	chdir (char const *path)
	Changes the current working directory to the given path. More...

int	fchdir (int fd)
	Is identical to chdir(), the only difference is that the directory is given as an open file descriptor. More...

ssize_t	getdents (int fd, dirent_t *dirp, unsigned int count)

int	dup (int fd)
	Return a new file descriptor. More...

unsigned	alarm (int seconds)
	Send signal to calling thread after desired seconds. More...

int	chmod (const char *pathname, mode_t mode)
	Change the file's mode bits. More...

int	fchmod (int fd, mode_t mode)
	Change the file's mode bits. More...

int	chown (const char *pathname, uid_t owner, gid_t group)
	Change the owner and group of a file. More...

int	fchown (int fd, uid_t owner, gid_t group)
	Change the owner and group of a file. More...

int	lchown (const char *pathname, uid_t owner, gid_t group)
	Change the owner and group of a file. More...

Detailed Description

Functions used to manage files.

Copyright: (c) 2014-2024 This file is distributed under the MIT License. See LICENSE.md for details.

Function Documentation

◆ alarm()

unsigned alarm ( int seconds )

Send signal to calling thread after desired seconds.

Parameters

seconds the amount of seconds.

Returns: If there is a previous alarm() request with time remaining, alarm() shall return a non-zero value that is the number of seconds until the previous request would have generated a SIGALRM signal. Otherwise, alarm() shall return 0.

◆ chdir()

int chdir ( char const * path )

Changes the current working directory to the given path.

Parameters

path	The new current working directory.

Returns: 0 on success, -1 on failure and errno is set to indicate the error.

◆ chmod()

int chmod	(	const char *	pathname,
		mode_t	mode
	)

Change the file's mode bits.

Parameters

pathname	The pathname of the file to change mode.
mode	The mode bits to set.

Returns: On success, 0 is returned. On error, -1 is returned, and errno is set appropriately.

◆ chown()

int chown	(	const char *	pathname,
		uid_t	owner,
		gid_t	group
	)

Change the owner and group of a file.

Parameters

pathname	The pathname of the file to change.
owner	The new owner to set.
group	The new group to set.

Returns: On success, 0 is returned. On error, -1 is returned, and errno is set appropriately.

◆ close()

int close ( int fd )

Close a file descriptor.

Parameters

fd	The file descriptor.

Returns: The result of the operation.

◆ dup()

int dup ( int fd )

Return a new file descriptor.

Parameters

fd	The fd pointing to the opened file.

Returns: On success, a new file descriptor is returned. On error, -1 is returned, and errno is set appropriately.

◆ execl()

int execl	(	const char *	path,
		const char *	arg,
			...
	)

Replaces the current process image with a new process image (argument list).

Parameters

path	The absolute path to the binary file to execute.
arg	A list of one or more pointers to null-terminated strings that represent the argument list available to the executed program.
...	The argument list.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execle()

int execle	(	const char *	path,
		const char *	arg,
			...
	)

Replaces the current process image with a new process image (argument list).

Parameters

path	The absolute path to the binary file to execute.
arg	A list of one or more pointers to null-terminated strings that represent the argument list available to the executed program.
...	The argument list which contains as last argument the environment.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execlp()

int execlp	(	const char *	file,
		const char *	arg,
			...
	)

Replaces the current process image with a new process image (argument list).

Parameters

file	The name of the binary file to execute, which is searched inside the paths specified inside the PATH environmental variable.
arg	A list of one or more pointers to null-terminated strings that represent the argument list available to the executed program.
...	The argument list.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execlpe()

int execlpe	(	const char *	file,
		const char *	arg,
			...
	)

Replaces the current process image with a new process image (argument list).

Parameters

file	The name of the binary file to execute, which is searched inside the paths specified inside the PATH environmental variable.
arg	A list of one or more pointers to null-terminated strings that represent the argument list available to the executed program.
...	The argument list which contains as last argument the environment.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execv()

int execv	(	const char *	path,
		char *const	argv[]
	)

Replaces the current process image with a new process image (argument vector).

Parameters

path	The absolute path to the binary file to execute.
argv	A vector of one or more pointers to null-terminated strings that represent the argument list available to the executed program.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execve()

int execve	(	const char *	path,
		char *const	argv[],
		char *const	envp[]
	)

Replaces the current process image with a new process image (argument vector), allows the caller to specify the environment of the executed program via envp.

Parameters

path	The absolute path to the binary file to execute.
argv	A vector of one or more pointers to null-terminated strings that represent the argument list available to the executed program.
envp	A vector of one or more pointers to null-terminated strings that represent the environment list available to the executed program.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execvp()

int execvp	(	const char *	file,
		char *const	argv[]
	)

Replaces the current process image with a new process image (argument vector).

Parameters

file	The name of the binary file to execute, which is searched inside the paths specified inside the PATH environmental variable.
argv	A vector of one or more pointers to null-terminated strings that represent the argument list available to the executed program.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ execvpe()

int execvpe	(	const char *	file,
		char *const	argv[],
		char *const	envp[]
	)

Replaces the current process image with a new process image (argument vector), allows the caller to specify the environment of the executed program via envp.

Parameters

file	The name of the binary file to execute, which is searched inside the paths specified inside the PATH environmental variable.
argv	A vector of one or more pointers to null-terminated strings that represent the argument list available to the executed program.
envp	A vector of one or more pointers to null-terminated strings that represent the environment list available to the executed program.

Returns: Returns -1 only if an error has occurred, and sets errno.

◆ exit()

void exit ( int status )

Wrapper for exit system call.

Parameters

status The exit status.

◆ fchdir()

int fchdir ( int fd )

Is identical to chdir(), the only difference is that the directory is given as an open file descriptor.

Parameters

fd	The file descriptor of the open directory.

Returns: 0 on success, -1 on failure and errno is set to indicate the error.

◆ fchmod()

int fchmod	(	int	fd,
		mode_t	mode
	)

Change the file's mode bits.

Parameters

fd	The fd pointing to the opened file.
mode	The mode bits to set.

Returns: On success, 0 is returned. On error, -1 is returned, and errno is set appropriately.

◆ fchown()

int fchown	(	int	fd,
		uid_t	owner,
		gid_t	group
	)

Change the owner and group of a file.

Parameters

fd	The fd pointing to the opened file.
owner	The new owner to set.
group	The new group to set.

Returns: On success, 0 is returned. On error, -1 is returned, and errno is set appropriately.

◆ fork()

pid_t fork ( void )

Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is replaced by a call to ‘execve’.

Returns: Return -1 for errors, 0 to the new process, and the process ID of the new process to the old process.

◆ getcwd()

char* getcwd	(	char *	buf,
		size_t	size
	)

Get current working directory.

Parameters

buf	The array where the CWD will be copied.
size	The size of the array.

Returns: On success, returns the same pointer to buf. On failure, returnr NULL, and errno is set to indicate the error.

◆ getdents()

ssize_t getdents	(	int	fd,
		dirent_t *	dirp,
		unsigned int	count
	)

Provide access to the directory entries.

Parameters

fd	The fd pointing to the opened directory.
dirp	The buffer where de data should be placed.
count	The size of the buffer.

Returns: On success, the number of bytes read is returned. On end of directory, 0 is returned. On error, -1 is returned, and errno is set appropriately.

◆ getegid()

gid_t getegid ( void )

returns the effective group ID of the calling process.

Returns: GID of the current process

◆ geteuid()

uid_t geteuid ( void )

Returns the effective User ID of the calling process.

Returns: User ID of the current process.

◆ getgid()

gid_t getgid ( void )

returns the real group ID of the calling process.

Returns: GID of the current process

◆ getpgid()

pid_t getpgid ( pid_t pid )

returns the Process Group ID (PGID) of the process specified by pid. If pid is zero, the process ID of the calling process is used.

Parameters

pid	process of which we want to know the PGID.

Returns: the PGID of the specified process.

◆ getpid()

pid_t getpid ( void )

Returns the process ID (PID) of the calling process.

Returns: pid_t process identifier.

◆ getppid()

pid_t getppid ( void )

Returns the parent process ID (PPID) of the calling process.

Returns: pid_t parent process identifier.

◆ getsid()

pid_t getsid ( pid_t pid )

Return session id of the given process. If pid == 0 return the SID of the calling process If pid != 0 return the SID corresponding to the process having identifier == pid.

Parameters

pid	process identifier from wich we want the SID

Returns: On success return SID of the session Otherwise return -1 with errno set on: EPERM or ESRCH

◆ getuid()

uid_t getuid ( void )

Returns the real User ID of the calling process.

Returns: User ID of the current process.

◆ lchown()

int lchown	(	const char *	pathname,
		uid_t	owner,
		gid_t	group
	)

Change the owner and group of a file.

Parameters

pathname	The pathname of the file to change.
owner	The new owner to set.
group	The new group to set.

Returns: On success, 0 is returned. On error, -1 is returned, and errno is set appropriately.

◆ lseek()

off_t lseek	(	int	fd,
		off_t	offset,
		int	whence
	)

Repositions the file offset inside a file.

Parameters

fd	The file descriptor of the file.
offset	The offest to use for the operation.
whence	The type of operation.

Returns: Upon successful completion, returns the resulting offset location as measured in bytes from the beginning of the file. On error, the value (off_t) -1 is returned and errno is set to indicate the error.

◆ nice()

int nice ( int inc )

Adds inc to the nice value for the calling thread.

Parameters

inc	The value to add to the nice.

Returns: On success, the new nice value is returned. On error, -1 is returned, and errno is set appropriately.

◆ open()

int open	(	const char *	pathname,
		int	flags,
		mode_t	mode
	)

Opens the file specified by pathname.

Parameters

pathname	A pathname for a file.
flags	file status flags and file access modes of the open file description.
mode	the file mode bits be applied when a new file is created.

Returns: file descriptor number, -1 otherwise and errno is set to indicate the error.

◆ read()

ssize_t read	(	int	fd,
		void *	buf,
		size_t	nbytes
	)

Read data from a file descriptor.

Parameters

fd	The file descriptor.
buf	The buffer.
nbytes	The number of bytes to read.

Returns: The number of read characters.

◆ readlink()

int readlink	(	const char *	path,
		char *	buffer,
		size_t	bufsize
	)

Read the symbolic link, if present.

Parameters

path	the file for which we want to read the symbolic link information.
buffer	the buffer where we will store the symbolic link path.
bufsize	the size of the buffer.

Returns: The number of read characters on success, -1 otherwise and errno is set to indicate the error.

◆ reboot()

int reboot	(	int	magic1,
		int	magic2,
		unsigned int	cmd,
		void *	arg
	)

Reboots the system, or enables/disables the reboot keystroke.

Parameters

magic1	fails (with the error EINVAL) unless equals LINUX_REBOOT_MAGIC1.
magic2	fails (with the error EINVAL) unless equals LINUX_REBOOT_MAGIC2.
cmd	The command to send to the reboot.
arg	Argument passed with some specific commands.

Returns: For the values of cmd that stop or restart the system, a successful call to reboot() does not return. For the other cmd values, zero is returned on success. In all cases, -1 is returned on failure, and errno is set appropriately.

◆ setgid()

int setgid ( gid_t gid )

sets the group IDs of the calling process.

Parameters

gid	the Group ID to set

Returns: On success, zero is returned. Otherwise returns -1 with errno set to :EINVAL or EPERM

◆ setpgid()

int setpgid	(	pid_t	pid,
		pid_t	pgid
	)

Sets the Process Group ID (PGID) of the process specified by pid. If pid is zero, the process ID of the calling process is used.

Parameters

pid	process of which we want to set the PGID.
pgid	the PGID we want to set.

Returns: returns zero. On error, -1 is returned, and errno is set appropriately.

◆ setregid()

int setregid	(	gid_t	rgid,
		gid_t	egid
	)

sets the real and effective group IDs of the calling process.

Parameters

rgid	the new real Group ID.
egid	the effective real Group ID.

Returns: On success, zero is returned. Otherwise returns -1 with errno set EPERM

◆ setreuid()

int setreuid	(	uid_t	ruid,
		uid_t	euid
	)

Sets the effective and real User IDs of the calling process.

Parameters

ruid	the new real User ID.
euid	the effective real User ID.

Returns: On success, zero is returned. Otherwise returns -1 with errno set to EPERM

◆ setsid()

pid_t setsid ( void )

creates a new session if the calling process is not a process group leader. The calling process is the leader of the new session (i.e., its session ID is made the same as its process ID). The calling process also becomes the process group leader of a new process group in the session (i.e., its process group ID is made the same as its process ID).

Returns: On success return SID of the session just created Otherwise return -1 with errno : EPERM

◆ setuid()

int setuid ( uid_t uid )

Sets the User IDs of the calling process.

Parameters

uid	the new User ID.

Returns: On success, zero is returned. Otherwise returns -1 with errno set to :EINVAL or EPERM

◆ symlink()

int symlink	(	const char *	linkname,
		const char *	path
	)

Creates a symbolic link.

Parameters

linkname	the name of the link.
path	the entity it is linking to.

Returns: 0 on success, a negative number if fails and errno is set.

◆ unlink()

int unlink ( const char * path )

Delete a name and possibly the file it refers to.

Parameters

path	The path to the file.

Returns: 0 on success, -errno on failure.

◆ write()

ssize_t write	(	int	fd,
		const void *	buf,
		size_t	nbytes
	)

Write data into a file descriptor.

Parameters

fd	The file descriptor.
buf	The buffer collecting data to written.
nbytes	The number of bytes to write.

Returns: The number of written bytes.

Macros

Functions

Detailed Description

Function Documentation

◆ alarm()

◆ chdir()

◆ chmod()

◆ chown()

◆ close()

◆ dup()

◆ execl()

◆ execle()

◆ execlp()

◆ execlpe()

◆ execv()

◆ execve()

◆ execvp()

◆ execvpe()

◆ exit()

◆ fchdir()

◆ fchmod()

◆ fchown()

◆ fork()

◆ getcwd()

◆ getdents()

◆ getegid()

◆ geteuid()

◆ getgid()

◆ getpgid()

◆ getpid()

◆ getppid()

◆ getsid()

◆ getuid()

◆ lchown()

◆ lseek()

◆ nice()

◆ open()

◆ read()

◆ readlink()

◆ reboot()

◆ setgid()

◆ setpgid()

◆ setregid()

◆ setreuid()

◆ setsid()

◆ setuid()

◆ symlink()

◆ unlink()

◆ write()