Manpage of UNLINK

UNLINK

Section: Linux Programmer's Manual (2)
Updated: 2016-03-15
Index
 

NAME

unlink, unlinkat - delete a name and possibly the file it refers to  

SYNOPSIS

#include <unistd.h>int unlink(const char *pathname);#include <fcntl.h>           /* Definition of AT_* constants */
#include <unistd.h>int unlinkat(int dirfd, const char *pathname, int flags);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

unlinkat():

Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_ATFILE_SOURCE
 

DESCRIPTION

unlink() deletes a name from the filesystem. If that name was the last link to a file and no processes have the file open, the file is deleted and the space it was using is made available for reuse.

If the name was the last link to a file but any processes still have the file open, the file will remain in existence until the last file descriptor referring to it is closed.

If the name referred to a symbolic link, the link is removed.

If the name referred to a socket, FIFO, or device, the name for it is removed but processes which have the object open may continue to use it.  

unlinkat()

The unlinkat() system call operates in exactly the same way as either unlink() or rmdir(2) (depending on whether or not flagsincludes the AT_REMOVEDIRflag) except for the differences described here.

If the pathname given in pathnameis relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd(rather than relative to the current working directory of the calling process, as is done by unlink() and rmdir(2) for a relative pathname).

If the pathname given in pathnameis relative and dirfdis the special value AT_FDCWD, then pathnameis interpreted relative to the current working directory of the calling process (like unlink() and rmdir(2)).

If the pathname given in pathnameis absolute, then dirfdis ignored.

flagsis a bit mask that can either be specified as 0, or by ORing together flag values that control the operation of unlinkat(). Currently, only one such flag is defined:

AT_REMOVEDIR
By default, unlinkat() performs the equivalent of unlink() on pathname. If the AT_REMOVEDIRflag is specified, then performs the equivalent of rmdir(2) on pathname.

See openat(2) for an explanation of the need for unlinkat().  

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errnois set appropriately.  

ERRORS

EACCES
Write access to the directory containing pathnameis not allowed for the process's effective UID, or one of the directories in pathnamedid not allow search permission. (See also path_resolution(7).)
EBUSY
The file pathnamecannot be unlinked because it is being used by the system or another process; for example, it is a mount point or the NFS client software created it to represent an active but otherwise nameless inode ("NFS silly renamed").
EFAULT
pathnamepoints outside your accessible address space.
EIO
An I/O error occurred.
EISDIR
pathnamerefers to a directory. (This is the non-POSIX value returned by Linux since 2.1.132.)
ELOOP
Too many symbolic links were encountered in translating pathname.
ENAMETOOLONG
pathname was too long.
ENOENT
A component in pathnamedoes not exist or is a dangling symbolic link, or pathnameis empty.
ENOMEM
Insufficient kernel memory was available.
ENOTDIR
A component used as a directory in pathnameis not, in fact, a directory.
EPERM
The system does not allow unlinking of directories, or unlinking of directories requires privileges that the calling process doesn't have. (This is the POSIX prescribed error return; as noted above, Linux returns EISDIRfor this case.)
EPERM (Linux only)
The filesystem does not allow unlinking of files.
EPERM or EACCES
The directory containing pathnamehas the sticky bit (S_ISVTX) set and the process's effective UID is neither the UID of the file to be deleted nor that of the directory containing it, and the process is not privileged (Linux: does not have the CAP_FOWNERcapability).
EROFS
pathnamerefers to a file on a read-only filesystem.

The same errors that occur for unlink() and rmdir(2) can also occur for unlinkat(). The following additional errors can occur for unlinkat():

EBADF
dirfdis not a valid file descriptor.
EINVAL
An invalid flag value was specified in flags.
EISDIR
pathnamerefers to a directory, and AT_REMOVEDIRwas not specified in flags.
ENOTDIR
pathnameis relative and dirfdis a file descriptor referring to a file other than a directory.
 

VERSIONS

unlinkat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.  

CONFORMING TO

unlink(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.

unlinkat(): POSIX.1-2008.  

NOTES

 

Glibc notes

On older kernels where unlinkat() is unavailable, the glibc wrapper function falls back to the use of unlink(2) or rmdir(2). When pathnameis a relative pathname, glibc constructs a pathname based on the symbolic link in /proc/self/fdthat corresponds to the dirfdargument.  

BUGS

Infelicities in the protocol underlying NFS can cause the unexpected disappearance of files which are still being used.  

SEE ALSO

rm(1), chmod(2), link(2), mknod(2), open(2), rename(2), rmdir(2), mkfifo(3), remove(3), path_resolution(7), symlink(7)


 

Index

NAME
SYNOPSIS
DESCRIPTION
unlinkat()
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
NOTES
Glibc notes
BUGS
SEE ALSO

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Time: 22:27:41 GMT, June 20, 2016