chmod(2)																  chmod(2)

NAME

       chmod, fchmod - change access permission mode of file

SYNOPSIS

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

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

       int fchmod(int fildes, mode_t mode);

       The  chmod()  and fchmod() functions set the access permission portion of the mode of the file whose name is given by path or referenced by
       the open file descriptor fildes to the bit pattern contained in mode. Access permission bits are interpreted as follows:

       S_ISUID	    04000     Set user ID on execution.
       S_ISGID	    020#0     Set group ID on execution if #  is  7,
			      5,   3,	or   1.   Enable   mandatory
			      file/record locking if # is 6,  4,  2,
			      or 0.
       S_ISVTX	    01000     Sticky bit.
       S_IRWXU	    00700     Read, write, execute by owner.
       S_IRUSR	    00400     Read by owner.
       S_IWUSR	    00200     Write by owner.
       S_IXUSR	    00100     Execute  (search	if  a  directory) by
			      owner.
       S_IRWXG	    00070     Read, write, execute by group.
       S_IRGRP	    00040     Read by group.
       S_IWGRP	    00020     Write by group.
       S_IXGRP	    00010     Execute by group.
       S_IRWXO	    00007     Read, write, execute (search) by	oth-
			      ers.
       S_IROTH	    00004     Read by others.
       S_IWOTH	    00002     Write by others.
       S_IXOTH	    00001     Execute by others.

       Modes are constructed by the bitwise OR operation of the access permission bits.

       The effective user ID of the process must match the owner of the file or the process must have the appropriate privilege to change the mode
       of a file.

       If the process is not a privileged process and the file is not a directory, mode bit 01000 (save text image on execution) is cleared.

       If neither the process is privileged nor the file's group is a member of the process's  supplementary group list, and the  effective  group
       ID of the process does not match the group ID of the file, mode bit 02000 (set group ID on execution) is cleared.

       If  a directory is writable and has S_ISVTX (the sticky bit) set, files within that directory can be removed or renamed only if one or more
       of the following is true (see unlink(2) and rename(2)):

	 o  the user owns the file

	 o  the user owns the directory

	 o  the file is writable by the user

	 o  the user is a privileged user

       If a regular file is not executable and has S_ISVTX set, the file is assumed to be a swap file. In this case, the system's page cache  will
       not be used to hold the file's data. If the S_ISVTX bit is set on any other file, the results are unspecified.

       If  a  directory  has  the  set group ID bit set, a given file created within that directory will have  the same group ID as the directory.
       Otherwise, the newly created file's group ID will be set to the effective group ID of the creating process.

       If the mode bit 02000 (set group ID on execution) is set and the mode bit 00010	(execute  or  search  by  group)  is  not  set,  mandatory
       file/record locking will exist on a regular file, possibly affecting future calls to open(2), creat(2), read(2), and write(2) on this file.

       If  fildes  references a shared memory object, fchmod() need only affect the S_IRUSR, S_IRGRP, S_IROTH, S_IWUSR, S_IWGRP, S_IWOTH, S_IXUSR,
       S_IXGRP, and S_IXOTH file permission bits.

       If fildes refers to a socket, fchmod() does not fail but no action is taken.

       If fildes refers to a STREAM that is attached to an object in the file system name space with fattach(3C), the fchmod()	call  performs	no
       action and returns successfully.

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

       Upon successful completion, 0 is returned. Otherwise, -1 is returned, the file mode is unchanged, and errno is set to indicate the error.

       The chmod() and fchmod() functions will fail if:

       EIO	       An I/O error occurred while reading from or writing to the file system.

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

		       The {PRIV_FILE_OWNER} privilege overrides constraints on ownership when changing permissions on a file.

		       The  {PRIV_FILE_SETID}  privilege overrides constraints on ownership when adding the setuid or setgid bits to an executable
		       file or a directory.  When adding the setuid bit to a root owned executable,  additional  restrictions  apply.  See  privi-
		       leges(5).

       The chmod() function will fail if:

       EACCES	       Search  permission is denied on a component of the path prefix of path. The privilege {FILE_DAC_SEARCH} overrides file per-
		       missions restrictions in that case.

       EFAULT	       The path argument points to an illegal address.

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

       ENAMETOOLONG    The length of the path argument exceeds PATH_MAX, or the length of a path component exceeds NAME_MAX while  _POSIX_NO_TRUNC
		       is in effect.

       ENOENT	       Either a component of the path prefix or the file referred to by path does not exist or is a null pathname.

       ENOLINK	       The fildes argument points to a remote machine and the link to that machine is no longer active.

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

       EROFS	       The file referred to by path resides on a read-only file system.

       The fchmod() function will fail if:

       EBADF	       The fildes argument is not an open file descriptor

       ENOLINK	       The path argument points to a remote machine and the link to that machine is no longer active.

       EROFS	       The file referred to by fildes resides on a read-only file system.

       The chmod() and fchmod() functions may fail if:

       EINTR	       A signal was caught during execution of the function.

       EINVAL	       The value of the mode argument is invalid.

       The chmod() function may fail if:

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

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

       The fchmod() function may fail if:

       EINVAL	       The fildes argument refers to a pipe and the system disallows execution of this function on a pipe.

       Example 1: Set 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);

       Example 2: Set 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);

       Example 3: Set 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);

       Example 4: Set and Checking File Permissions

       The  following example sets the file permission bits for a file named /home/cnd/mod1, then calls the stat(2) function to verify the permis-
       sions.

       #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;);

       If chmod() or fchmod() is used to change the file group owner permissions on a file with non-trivial ACL entries, only the ACL mask is  set
       to the new permissions and the group owner permission bits in the file's mode field (defined in mknod(2)) are unchanged.  A non-trivial ACL
       entry is one whose meaning cannot be represented in the file's mode field alone. The new ACL mask permissions  might change  the  effective
       permissions for additional users and groups that have ACL entries on the file.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

       chmod(1),  chown(2),  creat(2), fcntl(2), mknod(2), open(2), read(2), rename(2), stat(2), write(2), fattach(3C), mkfifo(3C), stat.h(3HEAD),
       attributes(5), privileges(5), standards(5)

								    12 Sep 2005 							  chmod(2)