Index for Section 2

Alphabetical listing for C

Bottom of page

chmod(2)
NAME
  chmod, fchmod - Change file access permissions

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

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

  #include <sys/stat.h>

  int fchmod(
	  int filedes,
	  mode_t mode );

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  chmod(): XSH4.0, XSH4.2, XSH5.0

  fchmod(): XSH4.2, XSH5.0

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  path
      Specifies the full pathname of the file. If the path parameter refers
      to a symbolic link, the chmod() function changes access permissions on
      the file specified by the symbolic link.

  filedes
      Specifies the file descriptor of an open file.

  mode
      Specifies the bit pattern that determines the access permissions.

DESCRIPTION
  The chmod() function sets the access permissions of the file specified by
  the path parameter according to the bit pattern specified by the mode
  parameter.

  The fchmod() function sets the access permissions of an open file pointed
  to by the filedes parameter according to the bit pattern specified by the
  mode parameter.

  To change file access permissions, the process must have the same effective
  user ID as the owner of the file or have superuser privilege.

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

  The mode parameter is constructed by logically ORing one or more of the
  following values, which are defined in the sys/mode.h header file:

  S_ISUID
      Sets the process' effective user ID to the file's owner on execution.

  S_ISGID
      Sets the process' effective group ID to the file's group on execution.

  S_ISVTX
      Saves text image after execution.

  S_IRWXU
      Permits the file's owner to read, write, and execute it (or to search
      the directory).

  S_IRUSR
      Permits the file's owner to read it.

  S_IWUSR
      Permits the file's owner to write to it.

  S_IXUSR
      Permits the file's owner to execute it (or to search the directory).

  S_IRWXG
      Permits the file's group to read, write, and execute it (or to search
      the directory).

  S_IRGRP
      Permits the file's group to read it.

  S_IWGRP
      Permits the file's group to write to it.

  S_IXGRP
      Permits the file's group to execute it (or to search the directory).

  S_IRWXO
      Permits others to read, write, and execute it (or to search the
      directory).

  S_IROTH
      Permits others to read the file.

  S_IWOTH
      Permits others to write to the file.

  S_IXOTH
      Permits others to execute the file (or to search the directory).

  Other mode values exist that can be set with the mknod() function, but not
  with the chmod() function.

  If the mode bit S_ISGID is set and the mode bit S_IXGRP is not set,
  mandatory file record locking will exist on a regular file. This may affect
  subsequent calls to other calls on the file, including open(), creat(),
  read(), write(), and truncate().

  The S_ISGID bit of the file is cleared if:

    ·  The file is a regular file.

    ·  The effective user ID of the process does not have appropriate system
       privilege.

    ·  The effective group ID or one of the IDs in the group access list of
       the process does not match the file's existing group ID.

RETURN VALUES
  Upon successful completion, the chmod() and fchmod() functions return a
  value of 0 (zero). If the chmod() or fchmod() function fails, a value of -1
  is returned, and errno is set to indicate the error.

ERRORS
  If the chmod() function fails, the file permissions remain unchanged and
  errno may be set to one of the following values:

  [EACCES]
      A component of the path parameter has search permission denied.

  [EFAULT]
      [Tru64 UNIX]  The path parameter points to a location outside of the
      allocated address space of the process.

  [EINTR]
      A signal was caught during execution of the system call.

  [EINVAL]
      The file is not a regular file.

  [ELOOP]
      Too many symbolic links were encountered in translating the path
      parameter.

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

  [ENOENT]
      The named file does not exist or is an empty string.

      A symbolic link was named, but the file to which it refers does not
      exist.

  [ENOTDIR]
      A component of the path parameter is not a directory.

  [EPERM]
      The effective user ID does not match the ID of the owner of the file or
      the owner does not have appropriate system privilege.

  [EROFS]
      The named file resides on a read-only file system

  [ESTALE]
      [Tru64 UNIX]  The process's root or current directory is located in a
      virtual file system that has been unmounted.

  If the fchmod() function fails, the file permissions remain unchanged and
  errno may be set to one of the following values:

  [EBADF]
      The file descriptor filedes is not valid.

  [EINTR]
      A signal was caught during execution of the system call.

  [EPERM]
      The effective user ID does not match the ID of the owner of the file,
      and the calling process does not have superuser privilege .

  [EROFS]
      The file referred to by filedes resides on a read-only file system.

  [ESTALE]
      [Tru64 UNIX]  The process' root or current directory is located in a
      virtual file system that has been unmounted.

SEE ALSO
  Functions:chown(2), fcntl(2), getgroups(2), mknod(2), open(2), read(2)
  setgroups(2) truncate(2) write(2)

  Commands:  chgrp(1), chmod(1)

  Others:  standards(5)

Index for Section 2

Alphabetical listing for C

Top of page