NAME

       chmod - change mode of a file

SYNOPSIS

       #include <sys/stat.h>

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

DESCRIPTION

       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.

       The effect on file descriptors for files open at the time of a call to chmod() is implementation-defined.

       Upon successful completion, chmod() shall mark for update the st_ctime field of the file.

RETURN VALUE

       Upon successful completion, 0 shall be returned; otherwise,  -1  shall  be  returned  and  errno  set  to
       indicate the error. If -1 is returned, no change to the file mode occurs.

ERRORS

       The chmod() function 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.

       ENAMETOOLONG
              The  length  of  the  path  argument  exceeds  {PATH_MAX}  or  a pathname component is longer than
              {NAME_MAX}.

       ENOTDIR
              A component of the path prefix is not a directory.

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

       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 chmod() function 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.

       ENAMETOOLONG
              As  a result of encountering a symbolic link in resolution of the path argument, the length of the
              substituted pathname strings exceeded {PATH_MAX}.

       The following sections are informative.

EXAMPLES

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

              #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"
              ...
              chmod(CHANGEFILE, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH);

   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 permissions.

              #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;);

APPLICATION USAGE

       In  order  to  ensure that the S_ISUID and S_ISGID bits are set, an application 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.

RATIONALE

       This  volume  of  IEEE Std 1003.1-2001  specifies that the S_ISGID bit is cleared by chmod() on a regular
       file under certain conditions. This is specified on the assumption that regular files  may  be  executed,
       and  the  system  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 function (for example, mandatory record
       locking) on non-executable files need not clear this bit on  writing.  They  should  clear  the  bit  for
       executable  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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       chown() , mkdir()  ,  mkfifo()  ,  open()  ,  stat()  ,  statvfs()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <sys/stat.h>, <sys/types.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 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 .

IEEE/The Open Group                                   2003                                              CHMOD(P)