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UNLINK(2) System Calls Manual UNLINK(2)

unlink, unlinkat — remove directory entry

library “libc”

#include <unistd.h>

int
unlink(const char *path);

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

The () system call 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 process 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 path argument may not be a directory.

The () system call is equivalent to unlink() or () except in the case where path specifies a relative path. In this case the directory entry to be removed is determined relative to the directory associated with the file descriptor fd instead of the current working directory.

The values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

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

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

The unlink() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The unlink() succeeds unless:

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A component of the path prefix is not a directory.
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The named file is a directory.
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A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
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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.
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The named file has its immutable, undeletable or append-only flag set, see the chflags(2) manual page for more information.
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The parent directory of the named file has its immutable or append-only flag set.
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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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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.
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The path argument points outside the process's allocated address space.
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On file systems supporting copy-on-write or snapshots, there was not enough free space to record metadata for the delete operation of the file.

In addition to the errors returned by the unlink(), the unlinkat() may fail if:

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The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for searching.
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The flag parameter has the AT_REMOVEDIR bit set and the path argument names a directory that is not an empty directory, or there are hard links to the directory other than dot or a single entry in dot-dot.
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The flag parameter has the AT_REMOVEDIR bit set and path does not name a directory.
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The value of the flag argument is not valid.
[]
The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

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

The unlinkat() system call follows The Open Group Extended API Set 2 specification.

The unlink() function appeared in Version 1 AT&T UNIX. The unlinkat() system call appeared in FreeBSD 8.0.

The unlink() system call traditionally allows the super-user to unlink directories which can damage the file system integrity. This implementation no longer permits it.

December 1, 2017 FreeBSD-12.0