chmod man page on Archlinux

Man page or keyword search:  
man Server   11224 pages
apropos Keyword Search (all sections)
Output format
Archlinux logo
[printable version]

CHMOD(3P)		   POSIX Programmer's Manual		     CHMOD(3P)

       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.

       chmod, fchmodat — change mode of a  file	 relative  to  directory  file

       #include <sys/stat.h>

       int chmod(const char *path, mode_t mode);
       int fchmodat(int fd, const char *path, mode_t mode, int flag);

       The  chmod()  function  shall change S_ISUID, S_ISGID, S_ISVTX, and the
       file permission bits of the file named by the pathname  pointed	to  by
       the  path  argument to the corresponding bits in the mode argument. The
       application shall ensure that the effective  user  ID  of  the  process
       matches the owner of the file or the process has appropriate privileges
       in order to do this.

       S_ISUID, S_ISGID, S_ISVTX, and the file permission bits	are  described
       in <sys/stat.h>.

       If the calling process does not have appropriate privileges, and if the
       group ID of the file does not match the effective group ID  or  one  of
       the  supplementary  group  IDs  and  if the file is a regular file, bit
       S_ISGID (set-group-ID on execution) in the file's mode shall be cleared
       upon successful return from chmod().

       Additional  implementation-defined  restrictions	 may cause the S_ISUID
       and S_ISGID bits in mode to be ignored.

       Upon successful completion, chmod() shall mark for update the last file
       status change timestamp of the file.

       The  fchmodat()	function  shall	 be equivalent to the chmod() function
       except in the case where path specifies a relative path. In  this  case
       the  file to be changed is determined relative to the directory associ‐
       ated with the file descriptor fd instead of the current working	direc‐
       tory.  If the file descriptor was opened without O_SEARCH, the function
       shall check whether directory searches are permitted using the  current
       permissions  of	the  directory	underlying the file descriptor. If the
       file descriptor was opened with O_SEARCH, the function shall  not  per‐
       form the check.

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

	     If path names a symbolic link, then the mode of the symbolic link
	     is changed.

       If fchmodat() is passed the special value AT_FDCWD in the fd parameter,
       the current working directory shall be used. If also flag is zero,  the
       behavior shall be identical to a call to chmod().

       Upon successful completion, these functions shall return 0.  Otherwise,
       these functions shall return −1 and set errno to indicate the error. If
       −1 is returned, no change to the file mode occurs.

       These functions shall fail if:

       EACCES Search permission is denied on a component of the path prefix.

       ELOOP  A loop exists in symbolic links encountered during resolution of
	      the path argument.

	      The  length  of  a  component  of	 a  pathname  is  longer  than

       ENOENT A component of path does not name an existing file or path is an
	      empty string.

	      A component of the path prefix names an existing	file  that  is
	      neither  a  directory nor a symbolic link to a directory, or the
	      path argument contains at least one  non-<slash>	character  and
	      ends  with  one or more trailing <slash> characters and the last
	      pathname component names an existing  file  that	is  neither  a
	      directory nor a symbolic link to a directory.

       EPERM  The  effective  user ID does not match the owner of the file and
	      the process does not have appropriate privileges.

       EROFS  The named file resides on a read-only file system.

       The fchmodat() function shall fail if:

       EACCES fd was not opened with  O_SEARCH	and  the  permissions  of  the
	      directory underlying fd do not permit directory searches.

       EBADF  The  path	 argument does not specify an absolute path and the fd
	      argument is neither AT_FDCWD nor a valid	file  descriptor  open
	      for reading or searching.

	      The  path	 argument  is  not  an	absolute path and fd is a file
	      descriptor associated with a non-directory file.

       These functions may fail if:

       EINTR  A signal was caught during execution of the function.

       EINVAL The value of the mode argument is invalid.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were  encountered	during
	      resolution of the path argument.

	      The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
	      tion of a symbolic link produced an intermediate result  with  a
	      length that exceeds {PATH_MAX}.

       The fchmodat() function may fail if:

       EINVAL The value of the flag argument is invalid.

	      The  AT_SYMLINK_NOFOLLOW	bit  is set in the flag argument, path
	      names a symbolic link, and the system does not support  changing
	      the mode of a symbolic link.

       The following sections are informative.

   Setting Read Permissions for User, Group, and Others
       The  following  example sets read permissions for the owner, group, and

	   #include <sys/stat.h>

	   const char *path;
	   chmod(path, S_IRUSR|S_IRGRP|S_IROTH);

   Setting Read, Write, and Execute Permissions for the Owner Only
       The following example sets read, write, and execute permissions for the
       owner, and no permissions for group and others.

	   #include <sys/stat.h>

	   const char *path;
	   chmod(path, S_IRWXU);

   Setting Different Permissions for Owner, Group, and Other
       The  following  example	sets owner permissions for CHANGEFILE to read,
       write, and execute, group permissions to read and  execute,  and	 other
       permissions to read.

	   #include <sys/stat.h>

	   #define CHANGEFILE "/etc/myfile"

   Setting and Checking File Permissions
       The  following  example	sets the file permission bits for a file named
       /home/cnd/mod1, then calls the stat() function to  verify  the  permis‐

	   #include <sys/types.h>
	   #include <sys/stat.h>

	   int status;
	   struct stat buffer
	   chmod("home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH);
	   status = stat("home/cnd/mod1", &buffer;);

       In order to ensure that the S_ISUID and S_ISGID bits are set, an appli‐
       cation requiring this should use stat() after a successful  chmod()  to
       verify this.

       Any  file  descriptors  currently open by any process on the file could
       possibly become invalid if the mode of the file is changed to  a	 value
       which would deny access to that process. One situation where this could
       occur is on a stateless file system. This behavior will not occur in  a
       conforming environment.

       This  volume  of POSIX.1‐2008 specifies that the S_ISGID bit is cleared
       by chmod() on a regular file under certain conditions. This  is	speci‐
       fied on the assumption that regular files may be executed, and the sys‐
       tem should prevent users from making executable setgid() files  perform
       with  privileges that the caller does not have. On implementations that
       support execution of other  file	 types,	 the  S_ISGID  bit  should  be
       cleared for those file types under the same circumstances.

       Implementations	that  use the S_ISUID bit to indicate some other func‐
       tion (for example, mandatory record locking)  on	 non-executable	 files
       need  not clear this bit on writing. They should clear the bit for exe‐
       cutable files and any other cases where the bit grants  special	powers
       to  processes  that change the file contents. Similar comments apply to
       the S_ISGID bit.

       The purpose of the fchmodat() function is to enable changing  the  mode
       of  files in directories other than the current working directory with‐
       out exposure to race conditions.	 Any part of the path of a file	 could
       be  changed  in parallel to a call to chmod(), resulting in unspecified
       behavior. By opening a file descriptor for  the	target	directory  and
       using  the  fchmodat()  function	 it can be guaranteed that the changed
       file is located relative to the desired directory. Some implementations
       might  allow changing the mode of symbolic links. This is not supported
       by the interfaces in the POSIX specification. Systems with such support
       provide	an  interface named lchmod().  To support such implementations
       fchmodat() has a flag parameter.


       access(), chown(),  exec,  fstatat(),  fstatvfs(),  mkdir(),  mkfifo(),
       mknod(), open()

       The  Base  Definitions volume of POSIX.1‐2008, <fcntl.h>, <sys_stat.h>,

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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 .

       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.ker‐ .

IEEE/The Open Group		     2013			     CHMOD(3P)

List of man pages available for Archlinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net