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chmod(2)				   System Calls 				 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);

DESCRIPTION
       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 others.
       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  direc-
       tory 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.

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

ERRORS
       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  permissions  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 resolu-
		       tion of the path argument.

       ENAMETOOLONG    As a result of encountering a symbolic link in resolution of thepath argu-
		       ment, 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.

EXAMPLES
       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 per-
       missions 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 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;);

USAGE
       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.

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

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

SEE ALSO
       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),  stan-
       dards(5)

       Programming Interfaces Guide

SunOS 5.11				   12 Sep 2005					 chmod(2)
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