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Base Operating System and Extensions Technical Reference, Volume 1
chmod or fchmod Subroutine
Purpose
Changes file access permissions.
Library
Standard C Library (libc.a)
Syntax
#include <sys/stat.h>
int chmod (Path, Mode)
const char *Path;
mode_t Mode;
int fchmod (FileDescriptor, Mode)
int FileDescriptor;
mode_t Mode;
Description
The chmod subroutine sets the access permissions of the file specified by the Path parameter. If Network File System (NFS) is installed on your
system, this path can cross into another node.
Use the fchmod subroutine to set the access permissions of an
open file pointed to by the FileDescriptor parameter.
The access control information is set according to the Mode
parameter.
Parameters
| FileDescriptor |
Specifies the file descriptor of an open file. |
| Mode |
Specifies the bit pattern that determines the access permissions. The Mode
parameter is constructed by logically ORing one or more of the following values, which are defined in
the sys/mode.h file:
- S_ISUID
- Enables the setuid attribute for an executable file. A process executing this program acquires the access rights of the owner of the file.
- S_ISGID
- Enables the setgid attribute for an executable file. A process executing this program acquires the access rights of the group of the file. Also, enables the group-inheritance attribute for a directory. Files created in this directory have a group equal to the group of the directory.
The following attributes apply only to files that are directly executable.
They have no meaning when applied to executable text files such as shell scripts and awk
scripts.
- S_ISVTX
- Enables the link/unlink attribute for a directory. Files cannot be linked to in this directory. Files can only be unlinked if the requesting process has write permission for the directory and is either the owner of the file or the directory.
- S_ISVTX
- Enables the save text attribute for an executable file. The program is not unmapped after usage.
- S_ENFMT
- Enables enforcement-mode record locking for a regular file. File locks requested with the lockf subroutine are enforced.
- 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_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_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 subroutine but not with the
chmod subroutine.
|
| Path |
Specifies the full path name of the file. |
Return Values
Upon successful completion, the chmod subroutine and
fchmod subroutines return a value of 0. If the chmod subroutine or fchmod
subroutine is unsuccessful, a value of -1 is returned, and the errno global variable is set to
identify the error.
Error Codes
The chmod subroutine is unsuccessful and the file
permissions remain unchanged if one of the following is true:
| ENOTDIR |
A component of the Path prefix is not a directory. |
| EACCES |
Search permission is denied on a component of the Path prefix. |
| EFAULT |
The Path parameter points to a location outside of the allocated address space of
the process. |
| ELOOP |
Too many symbolic links were encountered in translating the Path parameter. |
| ENOENT |
The named file does not exist. |
| ENAMETOOLONG |
A component of the Path parameter exceeded 255 characters, or the entire
Path parameter exceeded 1023 characters. |
| The fchmod subroutine is unsuccessful and the
file permissions remain unchanged if the following is true:
|
| EBADF |
The value of the FileDescriptor parameter is not valid. |
| The chmod or fchmod subroutine is
unsuccessful and the access control information for a file remains unchanged if one of the following
is true:
|
| 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. |
| EIO |
An I/O error occurred during the operation. |
| If NFS is installed on your system, the chmod
and fchmod subroutines can also be unsuccessful if the following is true:
|
| ESTALE |
The root or current directory of the process is located in a virtual file system that has
been unmounted. |
| ETIMEDOUT |
The connection timed out. |
Security
Access Control: The invoker must have search permission for all
components of the Path prefix.
If you receive the
EBUSY
error, toggle the
enforced locking
attribute in the
Mode
parameter and retry your operation. The
enforced locking
attribute should never be used on a file that is part of the Trusted Computing Base.
Implementation Specifics
These subroutines are part of Base Operating System (BOS)
Runtime.
Related Information
The acl_chg
subroutine, acl_get subroutine, acl_put subroutine, acl_set subroutine, chacl subroutine, statacl subroutine, stat subroutine.
The aclget command, aclput command, chmod command.
List of Security and Auditing
Subroutines and Subroutines
Overview in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs.
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