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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 inter-
preted 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 execu-
tion) is cleared.
SunOS 5.10 Last change: 12 Sep 2005 1
System Calls chmod(2)
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.
SunOS 5.10 Last change: 12 Sep 2005 2
System Calls chmod(2)
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 per-
missions 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 res-
trictions apply. See privileges(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
SunOS 5.10 Last change: 12 Sep 2005 3
System Calls chmod(2)
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.
SunOS 5.10 Last change: 12 Sep 2005 4
System Calls chmod(2)
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.
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 permis-
sions for the owner, and no permissions for group and oth-
ers.
#include <sys/stat.h>
const char *path;
...
chmod(path, S_IRWXU);
SunOS 5.10 Last change: 12 Sep 2005 5
System Calls chmod(2)
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 attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
| MT-Level | Async-Signal-Safe |
|_____________________________|_____________________________|
SunOS 5.10 Last change: 12 Sep 2005 6
System Calls chmod(2)
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),
standards(5)
Programming Interfaces Guide
SunOS 5.10 Last change: 12 Sep 2005 7
Man(1) output converted with
man2html and wrapped by fishsponge
This page was generated on Wed Sep 12 11:26:56 GMT 2007
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