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UNLINK(2) System Calls Manual UNLINK(2)

unlink, unlinkat — remove directory entry

#include <unistd.h>

int
unlink(const char *path);

#include <fcntl.h>
#include <unistd.h>

int
unlinkat(int fd, const char *path, int flag);

The () function removes the link named by path from its directory and decrements the link count of the file which was referenced by the link. If that decrement reduces the link count of the file to zero, and no process has the file open, then all resources associated with the file are reclaimed. If one or more processes have the file open when the last link is removed, the link is removed, but the removal of the file is delayed until all references to it have been closed.

The () function is equivalent to either the unlink() or rmdir(2) function depending on the value of flag (see below), except that where path specifies a relative path, the directory entry to be removed is determined relative to the directory associated with file descriptor fd instead of the current working directory.

If () is passed the special value AT_FDCWD (defined in <fcntl.h>) in the fd parameter, the current working directory is used and the behavior is identical to a call to unlink() or rmdir(2), depending on whether or not the AT_REMOVEDIR bit is set in flag.

The flag argument is the bitwise OR of zero or more of the following values:

Remove the directory entry specified by path as a directory, not a normal file.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The unlink() and unlinkat() functions will fail if:

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A component of the path prefix is not a directory.
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A component of a pathname exceeded NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded PATH_MAX bytes.
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The named file does not exist.
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Search permission is denied for a component of the path prefix.
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Write permission is denied on the directory containing the link to be removed.
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Too many symbolic links were encountered in translating the pathname.
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The named file is a directory and the effective user ID of the process is not the superuser, or the file system containing the file does not permit the use of unlink() on a directory.
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The directory containing the file is marked sticky, and neither the containing directory nor the file to be removed are owned by the effective user ID.
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The named file or the directory containing it has its immutable or append-only flag set (see chflags(2)).
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The entry to be unlinked is the mount point for a mounted file system.
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An I/O error occurred while deleting the directory entry or deallocating the inode.
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The named file resides on a read-only file system.
[]
path points outside the process's allocated address space.

Additionally, unlinkat() will fail if:

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The AT_REMOVEDIR flag bit is set and path does not name a directory.
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The AT_REMOVEDIR flag bit is set and the named directory contains files other than ‘.’ and ‘..’ in it.
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The value of the flag argument was neither zero nor AT_REMOVEDIR.
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The value of the flag argument was AT_REMOVEDIR and the last element of path consists of ‘.’.
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The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
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The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
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The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

rm(1), chflags(2), close(2), link(2), rmdir(2), symlink(7)

The unlink() and unlinkat() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

The unlink() system call first appeared in Version 1 AT&T UNIX. The unlinkat() function appeared in OpenBSD 5.0.

June 1, 2016 OpenBSD-6.6