symlink.3p (8184B)
- '\" et
- .TH SYMLINK "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .SH NAME
- symlink, symlinkat
- \(em make a symbolic link
- .SH SYNOPSIS
- .LP
- .nf
- #include <unistd.h>
- .P
- int symlink(const char *\fIpath1\fP, const char *\fIpath2\fP);
- .P
- #include <fcntl.h>
- .P
- int symlinkat(const char *\fIpath1\fP, int \fIfd\fP, const char *\fIpath2\fP);
- .fi
- .SH DESCRIPTION
- The
- \fIsymlink\fR()
- function shall create a symbolic link called
- .IR path2
- that contains the string pointed to by
- .IR path1
- (\c
- .IR path2
- is the name of the symbolic link created,
- .IR path1
- is the string contained in the symbolic link).
- .P
- The string pointed to by
- .IR path1
- shall be treated only as a string and shall not be validated
- as a pathname.
- .P
- If the
- \fIsymlink\fR()
- function fails for any reason other than
- .BR [EIO] ,
- any file named by
- .IR path2
- shall be unaffected.
- .P
- If
- .IR path2
- names a symbolic link,
- \fIsymlink\fR()
- shall fail and set
- .IR errno
- to
- .BR [EEXIST] .
- .P
- The symbolic link's user ID shall be set to the process' effective
- user ID. The symbolic link's group ID shall be set to the group
- ID of the parent directory or to the effective group ID of the
- process. Implementations shall provide a way to initialize the symbolic
- link's group ID to the group ID of the parent directory. Implementations
- may, but need not, provide an implementation-defined way to initialize the
- symbolic link's group ID to the effective group ID of the calling process.
- .P
- The values of the file mode bits for the created symbolic link are
- unspecified. All interfaces specified by POSIX.1\(hy2008 shall behave as if the
- contents of symbolic links can always be read, except that the value of
- the file mode bits returned in the
- .IR st_mode
- field of the
- .BR stat
- structure is unspecified.
- .P
- Upon successful completion,
- \fIsymlink\fR()
- shall mark for update the last data access, last data modification,
- and last file status change timestamps of the symbolic link. Also,
- the last data modification and last file status change timestamps of
- the directory that contains the new entry shall be marked for update.
- .P
- The
- \fIsymlinkat\fR()
- function shall be equivalent to the
- \fIsymlink\fR()
- function except in the case where
- .IR path2
- specifies a relative path. In this case the symbolic link is created
- relative to the directory associated with the file descriptor
- .IR fd
- instead of the current working directory. If the access mode of the
- open file description associated with the file descriptor is not
- O_SEARCH, the function shall check whether directory searches are
- permitted using the current permissions of the directory underlying
- the file descriptor. If the access mode is O_SEARCH, the function
- shall not perform the check.
- .P
- If
- \fIsymlinkat\fR()
- is passed the special value AT_FDCWD in the
- .IR fd
- parameter, the current working directory shall be used and the behavior
- shall be identical to a call to
- \fIsymlink\fR().
- .SH "RETURN VALUE"
- Upon successful completion, these functions shall return 0.
- Otherwise, these functions shall return \-1 and set
- .IR errno
- to indicate the error.
- .SH ERRORS
- These functions shall fail if:
- .TP
- .BR EACCES
- Write permission is denied in the directory where the symbolic link is
- being created, or search permission is denied for a component of the
- path prefix of
- .IR path2 .
- .TP
- .BR EEXIST
- The
- .IR path2
- argument names an existing file.
- .TP
- .BR EIO
- An I/O error occurs while reading from or writing to the file system.
- .TP
- .BR ELOOP
- A loop exists in symbolic links encountered during resolution of the
- .IR path2
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- The length of a component of the pathname specified by the
- .IR path2
- argument is longer than
- {NAME_MAX}
- or the length of the
- .IR path1
- argument is longer than
- {SYMLINK_MAX}.
- .TP
- .BR ENOENT
- A component of the path prefix of
- .IR path2
- does not name an existing file or
- .IR path2
- is an empty string.
- .TP
- .BR ENOENT " or " ENOTDIR
- .br
- The
- .IR path2
- argument contains at least one non-\c
- <slash>
- character and ends with one or more trailing
- <slash>
- characters. If
- .IR path2
- without the trailing
- <slash>
- characters would name an existing file, an
- .BR [ENOENT]
- error shall not occur.
- .TP
- .BR ENOSPC
- The directory in which the entry for the new symbolic link is being
- placed cannot be extended because no space is left on the file system
- containing the directory, or the new symbolic link cannot be created
- because no space is left on the file system which shall contain the
- link, or the file system is out of file-allocation resources.
- .TP
- .BR ENOTDIR
- A component of the path prefix of
- .IR path2
- names an existing file that is neither a directory nor a symbolic link
- to a directory.
- .TP
- .BR EROFS
- The new symbolic link would reside on a read-only file system.
- .P
- The
- \fIsymlinkat\fR()
- function shall fail if:
- .TP
- .BR EACCES
- The access mode of the open file description associated with
- .IR fd
- is not O_SEARCH and the permissions of the directory underlying
- .IR fd
- do not permit directory searches.
- .TP
- .BR EBADF
- The
- .IR path2
- argument does not specify an absolute path and the
- .IR fd
- argument is neither AT_FDCWD nor a valid file descriptor open for reading
- or searching.
- .TP
- .BR ENOTDIR
- The
- .IR path2
- argument is not an absolute path and
- .IR fd
- is a file descriptor associated with a non-directory file.
- .P
- These functions may fail if:
- .TP
- .BR ELOOP
- More than
- {SYMLOOP_MAX}
- symbolic links were encountered during resolution of the
- .IR path2
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- The length of the
- .IR path2
- argument exceeds
- {PATH_MAX}
- or pathname resolution of a symbolic link in the
- .IR path2
- argument produced an intermediate result with a length that exceeds
- {PATH_MAX}.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- Like a hard link, a symbolic link allows a file to have multiple
- logical names. The presence of a hard link guarantees the existence of
- a file, even after the original name has been removed. A symbolic link
- provides no such assurance; in fact, the file named by the
- .IR path1
- argument need not exist when the link is created. A symbolic link can
- cross file system boundaries.
- .P
- Normal permission checks are made on each component of the symbolic
- link pathname during its resolution.
- .SH RATIONALE
- The purpose of the
- \fIsymlinkat\fR()
- function is to create symbolic links in directories other than the
- current working directory without exposure to race conditions. Any part
- of the path of a file could be changed in parallel to a call to
- \fIsymlink\fR(),
- resulting in unspecified behavior. By opening a file descriptor for
- the target directory and using the
- \fIsymlinkat\fR()
- function it can be guaranteed that the created symbolic link is located
- relative to the desired directory.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIfdopendir\fR\^(\|)",
- .IR "\fIfstatat\fR\^(\|)",
- .IR "\fIlchown\fR\^(\|)",
- .IR "\fIlink\fR\^(\|)",
- .IR "\fIopen\fR\^(\|)",
- .IR "\fIreadlink\fR\^(\|)",
- .IR "\fIrename\fR\^(\|)",
- .IR "\fIunlink\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<fcntl.h>\fP",
- .IR "\fB<unistd.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 by the Institute of
- Electrical and Electronics Engineers, Inc and The Open Group.
- In the event of any discrepancy between this version and the original IEEE and
- The Open Group Standard, the original IEEE and The Open Group Standard
- is the referee document. The original Standard can be obtained online at
- http://www.opengroup.org/unix/online.html .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .