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The first routing protocol that was widely implemented, the Routing Information Protocol (RIP), calculated the shortest route based on geographic hops (the number of countries that an IP packet had to traverse to reach the destination host).
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unlinkat(2) [centos man page]

UNLINKAT(2)						     Linux Programmer's Manual						       UNLINKAT(2)

NAME
unlinkat - remove a directory entry relative to a directory file descriptor SYNOPSIS
#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: _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L Before glibc 2.10: _ATFILE_SOURCE DESCRIPTION
The unlinkat() system call operates in exactly the same way as either unlink(2) or rmdir(2) (depending on whether or not flags includes the AT_REMOVEDIR flag) except for the differences described in this manual page. 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(2) and rmdir(2) for a relative path- name). 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(2) 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(). Cur- rently only one such flag is defined: AT_REMOVEDIR By default, unlinkat() performs the equivalent of unlink(2) on pathname. If the AT_REMOVEDIR flag is specified, then performs the equivalent of rmdir(2) on pathname. RETURN VALUE
On success, unlinkat() returns 0. On error, -1 is returned and errno is set to indicate the error. ERRORS
The same errors that occur for unlink(2) and rmdir(2) can also occur for unlinkat(). The following additional errors can occur for unlinkat(): EBADF dirfd is not a valid file descriptor. EINVAL An invalid flag value was specified in flags. ENOTDIR pathname is relative and dirfd is 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
POSIX.1-2008. A similar system call exists on Solaris. NOTES
See openat(2) for an explanation of the need for unlinkat(). SEE ALSO
openat(2), rmdir(2), unlink(2), path_resolution(7) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2012-05-04 UNLINKAT(2)

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UNLINK(2)						     Linux Programmer's Manual							 UNLINK(2)

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 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 path- name). 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(). Cur- rently, only one such flag is defined: AT_REMOVEDIR 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 VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
EACCES Write access to the directory containing pathname is not allowed for the process's effective UID, or one of the directories in path- name did not allow search permission. (See also path_resolution(7).) EBUSY 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"). EFAULT pathname points outside your accessible address space. EIO An I/O error occurred. EISDIR pathname refers 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 pathname does not exist or is a dangling symbolic link, or pathname is empty. ENOMEM Insufficient kernel memory was available. ENOTDIR A component used as a directory in pathname is 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 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 capabil- ity). EPERM The file to be unlinked is marked immutable or append-only. (See ioctl_iflags(2).) EROFS 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(): EBADF dirfd is not a valid file descriptor. EINVAL An invalid flag value was specified in flags. EISDIR pathname refers to a directory, and AT_REMOVEDIR was not specified in flags. ENOTDIR pathname is relative and dirfd is 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() 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. BUGS
Infelicities in the protocol underlying NFS can cause the unexpected disappearance of files which are still being used. SEE ALSO
rm(1), unlink(1), chmod(2), link(2), mknod(2), open(2), rename(2), rmdir(2), mkfifo(3), remove(3), path_resolution(7), symlink(7) COLOPHON
This page is part of release 4.15 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/. Linux 2017-09-15 UNLINK(2)

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