2. System calls (functions provided by the kernel)
UNLINKSection: Linux Programmer's Manual (2)
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NAMEunlink, unlinkat - delete a name and possibly the file it refers to
#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)):
- Since glibc 2.10:
- _POSIX_C_SOURCE >= 200809L
- Before glibc 2.10:
DESCRIPTIONunlink() 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 flags includes the AT_REMOVEDIR flag) except for the differences described here.
If the pathname given in pathname is 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 pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted relative to the current working directory of the calling process (like unlink() and rmdir(2)).
If the pathname given in pathname is absolute, then dirfd is ignored.
flags is 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:
- By default, unlinkat() performs the equivalent of unlink() on pathname. If the AT_REMOVEDIR flag is specified, then performs the equivalent of rmdir(2) on pathname.
See openat(2) for an explanation of the need for unlinkat().
RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- Write access to the directory containing pathname is not allowed for the process's effective UID, or one of the directories in pathname did not allow search permission. (See also path_resolution(7).)
- The file pathname cannot 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").
- pathname points outside your accessible address space.
- An I/O error occurred.
- pathname refers to a directory. (This is the non-POSIX value returned by Linux since 2.1.132.)
- Too many symbolic links were encountered in translating pathname.
- pathname was too long.
- A component in pathname does not exist or is a dangling symbolic link, or pathname is empty.
- Insufficient kernel memory was available.
- A component used as a directory in pathname is not, in fact, a directory.
- 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 EISDIR for this case.)
- EPERM (Linux only)
- The filesystem does not allow unlinking of files.
- EPERM or EACCES
- The directory containing pathname has 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_FOWNER capability).
- The file to be unlinked is marked immutable or append-only. (See ioctl_iflags(2).)
- pathname refers 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():
- dirfd is not a valid file descriptor.
- An invalid flag value was specified in flags.
- pathname refers to a directory, and AT_REMOVEDIR was not specified in flags.
- pathname is relative and dirfd is a file descriptor referring to a file other than a directory.
VERSIONSunlinkat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.
CONFORMING TOunlink(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
Glibc notesOn older kernels where unlinkat() is unavailable, the glibc wrapper function falls back to the use of unlink() or rmdir(2). When pathname is a relative pathname, glibc constructs a pathname based on the symbolic link in /proc/self/fd that corresponds to the dirfd argument.
BUGSInfelicities in the protocol underlying NFS can cause the unexpected disappearance of files which are still being used.
SEE ALSOrm(1), unlink(1), chmod(2), link(2), mknod(2), open(2), rename(2), rmdir(2), mkfifo(3), remove(3), path_resolution(7), symlink(7)
COLOPHONThis page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
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