1UNLINK(3P) POSIX Programmer's Manual UNLINK(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 unlink - remove a directory entry
13
15 #include <unistd.h>
16 int unlink(const char *path);
18
21 The unlink() function shall remove a link to a file. If path names a
22 symbolic link, unlink() shall remove the symbolic link named by path
23 and shall not affect any file or directory named by the contents of the
24 symbolic link. Otherwise, unlink() shall remove the link named by the
25 pathname pointed to by path and shall decrement the link count of the
26 file referenced by the link.
27 When the file's link count becomes 0 and no process has the file open,
29 the space occupied by the file shall be freed and the file shall no
30 longer be accessible. If one or more processes have the file open when
31 the last link is removed, the link shall be removed before unlink()
32 returns, but the removal of the file contents shall be postponed until
33 all references to the file are closed.
34 The path argument shall not name a directory unless the process has
36 appropriate privileges and the implementation supports using unlink()
37 on directories.
38 Upon successful completion, unlink() shall mark for update the st_ctime
40 and st_mtime fields of the parent directory. Also, if the file's link
41 count is not 0, the st_ctime field of the file shall be marked for
42 update.
43
45 Upon successful completion, 0 shall be returned. Otherwise, -1 shall be
46 returned and errno set to indicate the error. If -1 is returned, the
47 named file shall not be changed.
48
50 The unlink() function shall fail and shall not unlink the file if:
51 EACCES Search permission is denied for a component of the path prefix,
53 or write permission is denied on the directory containing the
54 directory entry to be removed.
55 EBUSY The file named by the path argument cannot be unlinked because
57 it is being used by the system or another process and the imple‐
58 mentation considers this an error.
59 ELOOP A loop exists in symbolic links encountered during resolution of
61 the path argument.
62 ENAMETOOLONG
64 The length of the path argument exceeds {PATH_MAX} or a pathname
65 component is longer than {NAME_MAX}.
66 ENOENT A component of path does not name an existing file or path is an
68 empty string.
69 ENOTDIR
71 A component of the path prefix is not a directory.
72 EPERM The file named by path is a directory, and either the calling
74 process does not have appropriate privileges, or the implementa‐
75 tion prohibits using unlink() on directories.
76 EPERM or EACCES
78 The S_ISVTX flag is set on the directory containing the file
80 referred to by the path argument and the caller is not the file
81 owner, nor is the caller the directory owner, nor does the call‐
82 er have appropriate privileges.
83 EROFS The directory entry to be unlinked is part of a read-only file
85 system.
86 The unlink() function may fail and not unlink the file if:
89 EBUSY The file named by path is a named STREAM.
91 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
93 resolution of the path argument.
94 ENAMETOOLONG
96 As a result of encountering a symbolic link in resolution of the
97 path argument, the length of the substituted pathname string
98 exceeded {PATH_MAX}.
99 ETXTBSY
101 The entry to be unlinked is the last directory entry to a pure
102 procedure (shared text) file that is being executed.
103 The following sections are informative.
106
108 Removing a Link to a File
109 The following example shows how to remove a link to a file named
110 /home/cnd/mod1 by removing the entry named /modules/pass1.
111 #include <unistd.h>
114 char *path = "/modules/pass1";
117 int status;
118 ...
119 status = unlink(path);
120 Checking for an Error
122 The following example fragment creates a temporary password lock file
123 named LOCKFILE, which is defined as /etc/ptmp, and gets a file descrip‐
124 tor for it. If the file cannot be opened for writing, unlink() is used
125 to remove the link between the file descriptor and LOCKFILE.
126 #include <sys/types.h>
129 #include <stdio.h>
130 #include <fcntl.h>
131 #include <errno.h>
132 #include <unistd.h>
133 #include <sys/stat.h>
134 #define LOCKFILE "/etc/ptmp"
137 int pfd; /* Integer for file descriptor returned by open call. */
140 FILE *fpfd; /* File pointer for use in putpwent(). */
141 ...
142 /* Open password Lock file. If it exists, this is an error. */
143 if ((pfd = open(LOCKFILE, O_WRONLY| O_CREAT | O_EXCL, S_IRUSR
144 | S_IWUSR | S_IRGRP | S_IROTH)) == -1) {
145 fprintf(stderr, "Cannot open /etc/ptmp. Try again later.\n");
146 exit(1);
147 }
148 /* Lock file created; proceed with fdopen of lock file so that
151 putpwent() can be used.
152 */
153 if ((fpfd = fdopen(pfd, "w")) == NULL) {
154 close(pfd);
155 unlink(LOCKFILE);
156 exit(1);
157 }
158 Replacing Files
160 The following example fragment uses unlink() to discard links to files,
161 so that they can be replaced with new versions of the files. The first
162 call removes the link to LOCKFILE if an error occurs. Successive calls
163 remove the links to SAVEFILE and PASSWDFILE so that new links can be
164 created, then removes the link to LOCKFILE when it is no longer needed.
165 #include <sys/types.h>
168 #include <stdio.h>
169 #include <fcntl.h>
170 #include <errno.h>
171 #include <unistd.h>
172 #include <sys/stat.h>
173 #define LOCKFILE "/etc/ptmp"
176 #define PASSWDFILE "/etc/passwd"
177 #define SAVEFILE "/etc/opasswd"
178 ...
179 /* If no change was made, assume error and leave passwd unchanged. */
180 if (!valid_change) {
181 fprintf(stderr, "Could not change password for user %s\n", user);
182 unlink(LOCKFILE);
183 exit(1);
184 }
185 /* Change permissions on new password file. */
188 chmod(LOCKFILE, S_IRUSR | S_IRGRP | S_IROTH);
189 /* Remove saved password file. */
192 unlink(SAVEFILE);
193 /* Save current password file. */
196 link(PASSWDFILE, SAVEFILE);
197 /* Remove current password file. */
200 unlink(PASSWDFILE);
201 /* Save new password file as current password file. */
204 link(LOCKFILE,PASSWDFILE);
205 /* Remove lock file. */
208 unlink(LOCKFILE);
209 exit(0);
212
214 Applications should use rmdir() to remove a directory.
215
217 Unlinking a directory is restricted to the superuser in many historical
218 implementations for reasons given in link() (see also rename()).
219 The meaning of [EBUSY] in historical implementations is "mount point
221 busy". Since this volume of IEEE Std 1003.1-2001 does not cover the
222 system administration concepts of mounting and unmounting, the descrip‐
223 tion of the error was changed to "resource busy". (This meaning is used
224 by some device drivers when a second process tries to open an exclusive
225 use device.) The wording is also intended to allow implementations to
226 refuse to remove a directory if it is the root or current working
227 directory of any process.
228
230 None.
231
233 close(), link(), remove(), rmdir(), the Base Definitions volume of
234 IEEE Std 1003.1-2001, <unistd.h>
235
237 Portions of this text are reprinted and reproduced in electronic form
238 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
239 -- Portable Operating System Interface (POSIX), The Open Group Base
240 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
241 Electrical and Electronics Engineers, Inc and The Open Group. In the
242 event of any discrepancy between this version and the original IEEE and
243 The Open Group Standard, the original IEEE and The Open Group Standard
244 is the referee document. The original Standard can be obtained online
245 at http://www.opengroup.org/unix/online.html .
246IEEE/The Open Group 2003 UNLINK(3P)