mirror of https://github.com/mkerrisk/man-pages
195 lines
4.7 KiB
Groff
195 lines
4.7 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified by Michael Haardt <michael@moria.de>
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.\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 1997-01-12 by Michael Haardt
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.\" <michael@cantor.informatik.rwth-aachen.de>: NFS details
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.\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\"
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.TH CHMOD 2 2004-06-23 "Linux 2.6.7" "Linux Programmer's Manual"
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.SH NAME
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chmod, fchmod \- change permissions of a file
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.SH SYNOPSIS
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.B #include <sys/types.h>
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.br
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.B #include <sys/stat.h>
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.sp
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.BI "int chmod(const char *" path ", mode_t " mode );
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.br
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.BI "int fchmod(int " fildes ", mode_t " mode );
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.SH DESCRIPTION
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The mode of the file given by
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.I path
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or referenced by
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.I fildes
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is changed.
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Modes are specified by
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.IR or'ing
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the following:
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.RS
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.TP 1.0i
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S_ISUID
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04000 set user ID on execution
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.TP
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S_ISGID
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02000 set group ID on execution
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.TP
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S_ISVTX
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01000 sticky bit
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.TP
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S_IRUSR
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00400 read by owner
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.TP
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S_IWUSR
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00200 write by owner
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.TP
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S_IXUSR
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00100 execute/search by owner
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.TP
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S_IRGRP
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00040 read by group
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.TP
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S_IWGRP
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00020 write by group
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.TP
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S_IXGRP
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00010 execute/search by group
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.TP
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S_IROTH
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00004 read by others
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.TP
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S_IWOTH
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00002 write by others
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.TP
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S_IXOTH
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00001 execute/search by others
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.RE
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.PP
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The effective UID of the calling process must match the owner of the file,
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or the process must be privileged (Linux: it must have the
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.B CAP_FOWNER
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capability).
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If the calling process is not privileged (Linux: does not have the
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.B CAP_FSETID
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capability), and the group of the file does not match
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the effective group ID of the process or one of its
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supplementary group IDs, the S_ISGID bit will be turned off,
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but this will not cause an error to be returned.
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As a security measure, depending on the file system,
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the set-user-ID and set-group-ID execution bits
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may be turned off if a file is written.
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(On Linux this occurs if the writing process does not have the
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.B CAP_FSETID
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capability.)
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On some file systems, only the superuser can set the sticky bit,
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which may have a special meaning.
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For the sticky bit, and for set-user-ID and set-group-ID bits on
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directories, see
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.BR stat (2).
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On NFS file systems, restricting the permissions will immediately influence
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already open files, because the access control is done on the server, but
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open files are maintained by the client.
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Widening the permissions may be
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delayed for other clients if attribute caching is enabled on them.
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.SH "RETURN VALUE"
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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Depending on the file system, other errors can be returned.
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The more general errors for
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.BR chmod ()
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are listed below:
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.TP
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.B EACCES
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Search permission is denied on a component of the path prefix.
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(See also
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.BR path_resolution (2).)
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.TP
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.B EFAULT
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.I path
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points outside your accessible address space.
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.TP
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.B EIO
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An I/O error occurred.
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.TP
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.B ELOOP
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Too many symbolic links were encountered in resolving
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.IR path .
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.TP
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.B ENAMETOOLONG
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.I path
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is too long.
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.TP
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.B ENOENT
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The file does not exist.
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.TP
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.B ENOMEM
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Insufficient kernel memory was available.
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.TP
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.B ENOTDIR
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A component of the path prefix is not a directory.
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.TP
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.B EPERM
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The effective UID does not match the owner of the file,
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and the process is not privileged (Linux: it does not have the
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.B CAP_FOWNER
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capability).
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.TP
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.B EROFS
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The named file resides on a read-only file system.
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.PP
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The general errors for
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.BR fchmod ()
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are listed below:
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.TP
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.B EBADF
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The file descriptor
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.I fildes
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is not valid.
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.TP
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.B EIO
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See above.
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.TP
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.B EPERM
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See above.
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.TP
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.B EROFS
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See above.
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.SH "CONFORMING TO"
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4.4BSD, SVr4, POSIX.1-2001.
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.SH "SEE ALSO"
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.BR chown (2),
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.BR execve (2),
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.BR fchmodat (2),
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.BR open (2),
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.BR path_resolution (2),
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.BR stat (2)
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