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Manuál Linux
[Linux manuál]

chmod, fchmod: změnit oprávnění souboru

Originální popis anglicky: chmod, fchmod - change permissions of a file

Návod, kniha: Linux Programmer's Manual

STRUČNĚ

#include <sys/types.h>
 
#include <sys/stat.h>
 
int chmod(const char *path, mode_t mode);
 
int fchmod(int fildes, mode_t mode);

POPIS / INSTRUKCE

The mode of the file given by path or referenced by fildes is changed.
 
Modes are specified by or'ing the following:
 
S_ISUID
04000 set user ID on execution
S_ISGID
02000 set group ID on execution
S_ISVTX
01000 sticky bit
S_IRUSR (S_IREAD)
00400 read by owner
S_IWUSR (S_IWRITE)
00200 write by owner
S_IXUSR (S_IEXEC)
00100 execute/search by owner
S_IRGRP
00040 read by group
S_IWGRP
00020 write by group
S_IXGRP
00010 execute/search by group
S_IROTH
00004 read by others
S_IWOTH
00002 write by others
S_IXOTH
00001 execute/search by others
 
 
The effective UID of the calling process must match the owner of the file, or the process must be privileged (Linux: it must have the CAP_FOWNER capability).
 
If the calling process is not privileged (Linux: does not have the CAP_FSETID capability), and the group of the file does not match the effective group ID of the process or one of its supplementary group IDs, the S_ISGID bit will be turned off, but this will not cause an error to be returned.
 
As a security measure, depending on the file system, the set user ID and set group ID execution bits may be turned off if a file is written. (On Linux this occurs if the writing process does not have the CAP_FSETID capability.) On some file systems, only the super-user can set the sticky bit, which may have a special meaning. For the sticky bit, and for set user ID and set group ID bits on directories, see stat(2).
 
On NFS file systems, restricting the permissions will immediately influence already open files, because the access control is done on the server, but open files are maintained by the client. Widening the permissions may be delayed for other clients if attribute caching is enabled on them.

NÁVRATOVÁ HODNOTA

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

CHYBY / ERRORY

Depending on the file system, other errors can be returned. The more general errors for chmod are listed below:
 
EACCES
Search permission is denied on a component of the path prefix. (See also path_resolution(2).)
EFAULT
path points outside your accessible address space.
EIO
An I/O error occurred.
ELOOP
Too many symbolic links were encountered in resolving path.
ENAMETOOLONG
path is too long.
ENOENT
The file does not exist.
ENOMEM
Insufficient kernel memory was available.
ENOTDIR
A component of the path prefix is not a directory.
EPERM
The effective UID does not match the owner of the file, and the process is not privileged (Linux: it does not have the CAP_FOWNER capability).
EROFS
The named file resides on a read-only file system.
The general errors for fchmod are listed below:
EBADF
The file descriptor fildes is not valid.
EIO
See above.
EPERM
See above.
EROFS
See above.

ODPOVÍDAJÍCÍ

The chmod call conforms to SVr4, SVID, POSIX, X/OPEN, 4.4BSD. SVr4 documents EINTR, ENOLINK and EMULTIHOP returns, but no ENOMEM. POSIX.1 does not document EFAULT, ENOMEM, ELOOP or EIO error conditions, or the macros S_IREAD, S_IWRITE and S_IEXEC.
The fchmod call conforms to 4.4BSD and SVr4. SVr4 documents additional EINTR and ENOLINK error conditions. POSIX requires the fchmod function if at least one of _POSIX_MAPPED_FILES and _POSIX_SHARED_MEMORY_OBJECTS is defined, and documents additional ENOSYS and EINVAL error conditions, but does not document EIO.

SOUVISEJÍCÍ

chown(2), execve(2), open(2), path_resolution(2), stat(2)
2004-06-23 Linux 2.6.7
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