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* [patch] chmod.2, lchmod.3: Document lchmod()
@ 2021-01-10  4:37 Bruno Haible
  2021-01-10  7:41 ` Dmitry V. Levin
  0 siblings, 1 reply; 6+ messages in thread
From: Bruno Haible @ 2021-01-10  4:37 UTC (permalink / raw)
  To: mtk.manpages, linux-man

[-- Attachment #1: Type: text/plain, Size: 310 bytes --]

Hi,

lchmod (= the effect of fchmod with flag AT_SYMLINK_NOFOLLOW)
is implemented since glibc 2.32, see
https://sourceware.org/bugzilla/show_bug.cgi?id=14578
https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=752dd17443e55a4535cb9e6baa4e550ede383540

Here is a patch to update the man pages accordingly.



[-- Attachment #2: 0001-chmod.2-lchmod.3-Document-lchmod.patch --]
[-- Type: text/x-patch, Size: 2341 bytes --]

From 22cbd89a89bc26a518537739d677a5736727738f Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Sun, 10 Jan 2021 05:20:30 +0100
Subject: [PATCH] chmod.2, lchmod.3: Document lchmod().

---
 man2/chmod.2  | 25 +++++++++++++++++++++----
 man3/lchmod.3 |  1 +
 2 files changed, 22 insertions(+), 4 deletions(-)
 create mode 100644 man3/lchmod.3

diff --git a/man2/chmod.2 b/man2/chmod.2
index a54aec7..897dd87 100644
--- a/man2/chmod.2
+++ b/man2/chmod.2
@@ -29,15 +29,16 @@
 .\"   <michael@cantor.informatik.rwth-aachen.de>: NFS details
 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
 .\"
-.TH CHMOD 2 2017-09-15 "Linux" "Linux Programmer's Manual"
+.TH CHMOD 2 2021-01-10 "Linux" "Linux Programmer's Manual"
 .SH NAME
-chmod, fchmod, fchmodat \- change permissions of a file
+chmod, fchmod, lchmod, fchmodat \- change permissions of a file
 .SH SYNOPSIS
 .nf
 .B #include <sys/stat.h>
 .PP
 .BI "int chmod(const char *" pathname ", mode_t " mode );
 .BI "int fchmod(int " fd ", mode_t " mode );
+.BI "int lchmod(const char *" pathname ", mode_t " mode );
 .PP
 .BR "#include <fcntl.h>" "           /* Definition of AT_* constants */"
 .B #include <sys/stat.h>
@@ -68,6 +69,12 @@ Feature Test Macro Requirements for glibc (see
 .\"        || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
 .fi
 .PP
+.BR lchmod ():
+.nf
+    Since glibc 2.32:
+        _DEFAULT_SOURCE
+.fi
+.PP
 .BR fchmodat ():
 .nf
     Since glibc 2.10:
@@ -93,6 +100,11 @@ which is dereferenced if it is a symbolic link.
 .BR fchmod ()
 changes the mode of the file referred to by the open file descriptor
 .IR fd .
+.IP *
+.BR lchmod ()
+is like
+.BR chmod (),
+but does not dereference symbolic links.
 .PP
 The new file mode is specified in
 .IR mode ,
@@ -220,8 +232,13 @@ can either be 0, or include the following flag:
 If
 .I pathname
 is a symbolic link, do not dereference it:
-instead operate on the link itself.
-This flag is not currently implemented.
+instead operate on the link itself, like
+.BR lchmod ().
+(By default,
+.BR fchmodat ()
+dereferences symbolic links, like
+.BR chmod ().)
+This flag is implemented since glibc 2.32.
 .PP
 See
 .BR openat (2)
diff --git a/man3/lchmod.3 b/man3/lchmod.3
new file mode 100644
index 0000000..92647d2
--- /dev/null
+++ b/man3/lchmod.3
@@ -0,0 +1 @@
+.so man2/chmod.2
-- 
2.7.4


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [patch] chmod.2, lchmod.3: Document lchmod()
  2021-01-10  4:37 [patch] chmod.2, lchmod.3: Document lchmod() Bruno Haible
@ 2021-01-10  7:41 ` Dmitry V. Levin
  2021-01-10 10:05   ` Bruno Haible
  0 siblings, 1 reply; 6+ messages in thread
From: Dmitry V. Levin @ 2021-01-10  7:41 UTC (permalink / raw)
  To: Bruno Haible; +Cc: mtk.manpages, linux-man

Hi,

On Sun, Jan 10, 2021 at 05:37:13AM +0100, Bruno Haible wrote:
> Hi,
> 
> lchmod (= the effect of fchmod with flag AT_SYMLINK_NOFOLLOW)
> is implemented since glibc 2.32, see
> https://sourceware.org/bugzilla/show_bug.cgi?id=14578
> https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=752dd17443e55a4535cb9e6baa4e550ede383540
> 
> Here is a patch to update the man pages accordingly.

Please note the important limitation of that implementation:
it doesn't work when /proc is not mounted, see
https://sourceware.org/bugzilla/show_bug.cgi?id=26401


-- 
ldv

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [patch] chmod.2, lchmod.3: Document lchmod()
  2021-01-10  7:41 ` Dmitry V. Levin
@ 2021-01-10 10:05   ` Bruno Haible
  2021-01-10 17:50     ` Dmitry V. Levin
  2021-01-11  8:02     ` Michael Kerrisk (man-pages)
  0 siblings, 2 replies; 6+ messages in thread
From: Bruno Haible @ 2021-01-10 10:05 UTC (permalink / raw)
  To: Dmitry V. Levin; +Cc: mtk.manpages, linux-man

[-- Attachment #1: Type: text/plain, Size: 301 bytes --]

Dmitry V. Levin wrote:
> > Here is a patch to update the man pages accordingly.
> 
> Please note the important limitation of that implementation:
> it doesn't work when /proc is not mounted, see
> https://sourceware.org/bugzilla/show_bug.cgi?id=26401

Thanks for the pointer. Revised patch attached.


[-- Attachment #2: 0001-chmod.2-lchmod.3-Document-lchmod.patch --]
[-- Type: text/x-patch, Size: 4208 bytes --]

From 56ce64325fa9a9184b820eac908ecc5d53a5154b Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Sun, 10 Jan 2021 05:20:30 +0100
Subject: [PATCH] chmod.2, lchmod.3: Document lchmod().

---
 man2/chmod.2  | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 man3/lchmod.3 |  1 +
 2 files changed, 65 insertions(+), 6 deletions(-)
 create mode 100644 man3/lchmod.3

diff --git a/man2/chmod.2 b/man2/chmod.2
index a54aec7..f1709ef 100644
--- a/man2/chmod.2
+++ b/man2/chmod.2
@@ -29,15 +29,16 @@
 .\"   <michael@cantor.informatik.rwth-aachen.de>: NFS details
 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
 .\"
-.TH CHMOD 2 2017-09-15 "Linux" "Linux Programmer's Manual"
+.TH CHMOD 2 2021-01-10 "Linux" "Linux Programmer's Manual"
 .SH NAME
-chmod, fchmod, fchmodat \- change permissions of a file
+chmod, fchmod, lchmod, fchmodat \- change permissions of a file
 .SH SYNOPSIS
 .nf
 .B #include <sys/stat.h>
 .PP
 .BI "int chmod(const char *" pathname ", mode_t " mode );
 .BI "int fchmod(int " fd ", mode_t " mode );
+.BI "int lchmod(const char *" pathname ", mode_t " mode );
 .PP
 .BR "#include <fcntl.h>" "           /* Definition of AT_* constants */"
 .B #include <sys/stat.h>
@@ -68,6 +69,12 @@ Feature Test Macro Requirements for glibc (see
 .\"        || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
 .fi
 .PP
+.BR lchmod ():
+.nf
+    Since glibc 2.32:
+        _DEFAULT_SOURCE
+.fi
+.PP
 .BR fchmodat ():
 .nf
     Since glibc 2.10:
@@ -80,10 +87,12 @@ The
 .BR chmod ()
 and
 .BR fchmod ()
-system calls change a files mode bits.
+system calls and the
+.BR lchmod ()
+function change a file's mode bits.
 (The file mode consists of the file permission bits plus the set-user-ID,
 set-group-ID, and sticky bits.)
-These system calls differ only in how the file is specified:
+These functions differ only in how the file is specified:
 .IP * 2
 .BR chmod ()
 changes the mode of the file specified whose pathname is given in
@@ -93,6 +102,11 @@ which is dereferenced if it is a symbolic link.
 .BR fchmod ()
 changes the mode of the file referred to by the open file descriptor
 .IR fd .
+.IP *
+.BR lchmod ()
+is like
+.BR chmod (),
+but does not dereference symbolic links.
 .PP
 The new file mode is specified in
 .IR mode ,
@@ -220,8 +234,13 @@ can either be 0, or include the following flag:
 If
 .I pathname
 is a symbolic link, do not dereference it:
-instead operate on the link itself.
-This flag is not currently implemented.
+instead operate on the link itself, like
+.BR lchmod ().
+(By default,
+.BR fchmodat ()
+dereferences symbolic links, like
+.BR chmod ().)
+This flag is implemented since glibc 2.32.
 .PP
 See
 .BR openat (2)
@@ -304,6 +323,17 @@ See above.
 The same errors that occur for
 .BR chmod ()
 can also occur for
+.BR lchmod ().
+The following additional errors can occur for
+.BR lchmod ():
+.TP
+.B EOPNOTSUPP
+.B /proc
+is not mounted.
+.PP
+The same errors that occur for
+.BR chmod ()
+can also occur for
 .BR fchmodat ().
 The following additional errors can occur for
 .BR fchmodat ():
@@ -323,14 +353,31 @@ is relative and
 is a file descriptor referring to a file other than a directory.
 .TP
 .B ENOTSUP
+(Before glibc 2.32.)
 .I flags
 specified
 .BR AT_SYMLINK_NOFOLLOW ,
 which is not supported.
+.TP
+.B EOPNOTSUPP
+(Since glibc 2.32.)
+.I flags
+specified
+.BR AT_SYMLINK_NOFOLLOW ,
+and
+.B /proc
+is not mounted.
 .SH VERSIONS
 .BR fchmodat ()
 was added to Linux in kernel 2.6.16;
 library support was added to glibc in version 2.4.
+.PP
+.BR lchmod ()
+and the handling of
+.B AT_SYMLINK_NOFOLLOW
+in
+.BR fchmodat ()
+were added in glibc version 2.32.
 .SH CONFORMING TO
 .BR chmod (),
 .BR fchmod ():
@@ -362,6 +409,17 @@ glibc constructs a pathname based on the symbolic link in
 that corresponds to the
 .IR dirfd
 argument.
+.SH BUGS
+.BR lchmod ()
+and
+.BR fchmodat ()
+with
+.B AT_SYMLINK_NOFOLLOW
+flag fail with error
+.B EOPNOTSUPP
+when the
+.B /proc
+file system is not mounted.
 .SH SEE ALSO
 .BR chmod (1),
 .BR chown (2),
diff --git a/man3/lchmod.3 b/man3/lchmod.3
new file mode 100644
index 0000000..92647d2
--- /dev/null
+++ b/man3/lchmod.3
@@ -0,0 +1 @@
+.so man2/chmod.2
-- 
2.7.4


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [patch] chmod.2, lchmod.3: Document lchmod()
  2021-01-10 10:05   ` Bruno Haible
@ 2021-01-10 17:50     ` Dmitry V. Levin
  2021-01-11  8:02     ` Michael Kerrisk (man-pages)
  1 sibling, 0 replies; 6+ messages in thread
From: Dmitry V. Levin @ 2021-01-10 17:50 UTC (permalink / raw)
  To: Bruno Haible; +Cc: mtk.manpages, linux-man

On Sun, Jan 10, 2021 at 11:05:16AM +0100, Bruno Haible wrote:
> Dmitry V. Levin wrote:
> > > Here is a patch to update the man pages accordingly.
> > 
> > Please note the important limitation of that implementation:
> > it doesn't work when /proc is not mounted, see
> > https://sourceware.org/bugzilla/show_bug.cgi?id=26401
> 
> Thanks for the pointer. Revised patch attached.

LGTM, thanks.


-- 
ldv

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [patch] chmod.2, lchmod.3: Document lchmod()
  2021-01-10 10:05   ` Bruno Haible
  2021-01-10 17:50     ` Dmitry V. Levin
@ 2021-01-11  8:02     ` Michael Kerrisk (man-pages)
  2021-01-18 16:00       ` Michael Kerrisk (man-pages)
  1 sibling, 1 reply; 6+ messages in thread
From: Michael Kerrisk (man-pages) @ 2021-01-11  8:02 UTC (permalink / raw)
  To: Bruno Haible; +Cc: mtk.manpages, linux-man, Dmitry V. Levin

On 1/10/21 11:05 AM, Bruno Haible wrote:
> Dmitry V. Levin wrote:
>>> Here is a patch to update the man pages accordingly.
>>
>> Please note the important limitation of that implementation:
>> it doesn't work when /proc is not mounted, see
>> https://sourceware.org/bugzilla/show_bug.cgi?id=26401
> 
> Thanks for the pointer. Revised patch attached.

Hi Bruno,

Thank you for the patch.

But, I have a question: is lchown() actually usable? That is,
are there any kinds of links whose mode can be changed? I
can't seem to use it with normal symlinks, or for that matter, 
magic links:

[[
$ cat t_lchmod.c 
/*#* t_lchmod.c

   Copyright Michael Kerrisk,  Jan 2021
*/
#define _DEFAULT_SOURCE
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

typedef enum { FALSE, TRUE } Boolean;
int
main(int argc, char *argv[])
{
    if (argc < 2) {
	fprintf(stderr, "Usage: %s <file> <mode>\n", argv[0]);
	exit(EXIT_FAILURE);
    }

    int mode = strtoul(argv[2], NULL, 0);
    if (lchmod(argv[1], mode) == -1) {
        perror("lchmod");
	exit(EXIT_FAILURE);
    }

    exit(EXIT_SUCCESS);
}

$ touch a 
$ ln -s a b
$ ./t_lchmod b 700
lchmod: Operation not supported
$ ./t_lchmod /proc/self/fd/0 700
lchmod: Operation not supported
]]


Thanks,

Michael

=====


>From 56ce64325fa9a9184b820eac908ecc5d53a5154b Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Sun, 10 Jan 2021 05:20:30 +0100
Subject: [PATCH] chmod.2, lchmod.3: Document lchmod().

---
 man2/chmod.2  | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 man3/lchmod.3 |  1 +
 2 files changed, 65 insertions(+), 6 deletions(-)
 create mode 100644 man3/lchmod.3

diff --git a/man2/chmod.2 b/man2/chmod.2
index a54aec7..f1709ef 100644
--- a/man2/chmod.2
+++ b/man2/chmod.2
@@ -29,15 +29,16 @@
 .\"   <michael@cantor.informatik.rwth-aachen.de>: NFS details
 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
 .\"
-.TH CHMOD 2 2017-09-15 "Linux" "Linux Programmer's Manual"
+.TH CHMOD 2 2021-01-10 "Linux" "Linux Programmer's Manual"
 .SH NAME
-chmod, fchmod, fchmodat \- change permissions of a file
+chmod, fchmod, lchmod, fchmodat \- change permissions of a file
 .SH SYNOPSIS
 .nf
 .B #include <sys/stat.h>
 .PP
 .BI "int chmod(const char *" pathname ", mode_t " mode );
 .BI "int fchmod(int " fd ", mode_t " mode );
+.BI "int lchmod(const char *" pathname ", mode_t " mode );
 .PP
 .BR "#include <fcntl.h>" "           /* Definition of AT_* constants */"
 .B #include <sys/stat.h>
@@ -68,6 +69,12 @@ Feature Test Macro Requirements for glibc (see
 .\"        || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
 .fi
 .PP
+.BR lchmod ():
+.nf
+    Since glibc 2.32:
+        _DEFAULT_SOURCE
+.fi
+.PP
 .BR fchmodat ():
 .nf
     Since glibc 2.10:
@@ -80,10 +87,12 @@ The
 .BR chmod ()
 and
 .BR fchmod ()
-system calls change a files mode bits.
+system calls and the
+.BR lchmod ()
+function change a file's mode bits.
 (The file mode consists of the file permission bits plus the set-user-ID,
 set-group-ID, and sticky bits.)
-These system calls differ only in how the file is specified:
+These functions differ only in how the file is specified:
 .IP * 2
 .BR chmod ()
 changes the mode of the file specified whose pathname is given in
@@ -93,6 +102,11 @@ which is dereferenced if it is a symbolic link.
 .BR fchmod ()
 changes the mode of the file referred to by the open file descriptor
 .IR fd .
+.IP *
+.BR lchmod ()
+is like
+.BR chmod (),
+but does not dereference symbolic links.
 .PP
 The new file mode is specified in
 .IR mode ,
@@ -220,8 +234,13 @@ can either be 0, or include the following flag:
 If
 .I pathname
 is a symbolic link, do not dereference it:
-instead operate on the link itself.
-This flag is not currently implemented.
+instead operate on the link itself, like
+.BR lchmod ().
+(By default,
+.BR fchmodat ()
+dereferences symbolic links, like
+.BR chmod ().)
+This flag is implemented since glibc 2.32.
 .PP
 See
 .BR openat (2)
@@ -304,6 +323,17 @@ See above.
 The same errors that occur for
 .BR chmod ()
 can also occur for
+.BR lchmod ().
+The following additional errors can occur for
+.BR lchmod ():
+.TP
+.B EOPNOTSUPP
+.B /proc
+is not mounted.
+.PP
+The same errors that occur for
+.BR chmod ()
+can also occur for
 .BR fchmodat ().
 The following additional errors can occur for
 .BR fchmodat ():
@@ -323,14 +353,31 @@ is relative and
 is a file descriptor referring to a file other than a directory.
 .TP
 .B ENOTSUP
+(Before glibc 2.32.)
 .I flags
 specified
 .BR AT_SYMLINK_NOFOLLOW ,
 which is not supported.
+.TP
+.B EOPNOTSUPP
+(Since glibc 2.32.)
+.I flags
+specified
+.BR AT_SYMLINK_NOFOLLOW ,
+and
+.B /proc
+is not mounted.
 .SH VERSIONS
 .BR fchmodat ()
 was added to Linux in kernel 2.6.16;
 library support was added to glibc in version 2.4.
+.PP
+.BR lchmod ()
+and the handling of
+.B AT_SYMLINK_NOFOLLOW
+in
+.BR fchmodat ()
+were added in glibc version 2.32.
 .SH CONFORMING TO
 .BR chmod (),
 .BR fchmod ():
@@ -362,6 +409,17 @@ glibc constructs a pathname based on the symbolic link in
 that corresponds to the
 .IR dirfd
 argument.
+.SH BUGS
+.BR lchmod ()
+and
+.BR fchmodat ()
+with
+.B AT_SYMLINK_NOFOLLOW
+flag fail with error
+.B EOPNOTSUPP
+when the
+.B /proc
+file system is not mounted.
 .SH SEE ALSO
 .BR chmod (1),
 .BR chown (2),
diff --git a/man3/lchmod.3 b/man3/lchmod.3
new file mode 100644
index 0000000..92647d2
--- /dev/null
+++ b/man3/lchmod.3
@@ -0,0 +1 @@
+.so man2/chmod.2
-- 
2.7.4

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
yo

^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [patch] chmod.2, lchmod.3: Document lchmod()
  2021-01-11  8:02     ` Michael Kerrisk (man-pages)
@ 2021-01-18 16:00       ` Michael Kerrisk (man-pages)
  0 siblings, 0 replies; 6+ messages in thread
From: Michael Kerrisk (man-pages) @ 2021-01-18 16:00 UTC (permalink / raw)
  To: Bruno Haible; +Cc: mtk.manpages, linux-man, Dmitry V. Levin

Hi Bruno,

Ping!

Thanks,

Michael

On 1/11/21 9:02 AM, Michael Kerrisk (man-pages) wrote:
> On 1/10/21 11:05 AM, Bruno Haible wrote:
>> Dmitry V. Levin wrote:
>>>> Here is a patch to update the man pages accordingly.
>>>
>>> Please note the important limitation of that implementation:
>>> it doesn't work when /proc is not mounted, see
>>> https://sourceware.org/bugzilla/show_bug.cgi?id=26401
>>
>> Thanks for the pointer. Revised patch attached.
> 
> Hi Bruno,
> 
> Thank you for the patch.
> 
> But, I have a question: is lchown() actually usable? That is,
> are there any kinds of links whose mode can be changed? I
> can't seem to use it with normal symlinks, or for that matter, 
> magic links:
> 
> [[
> $ cat t_lchmod.c 
> /*#* t_lchmod.c
> 
>    Copyright Michael Kerrisk,  Jan 2021
> */
> #define _DEFAULT_SOURCE
> #include <sys/stat.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <string.h>
> 
> typedef enum { FALSE, TRUE } Boolean;
> int
> main(int argc, char *argv[])
> {
>     if (argc < 2) {
> 	fprintf(stderr, "Usage: %s <file> <mode>\n", argv[0]);
> 	exit(EXIT_FAILURE);
>     }
> 
>     int mode = strtoul(argv[2], NULL, 0);
>     if (lchmod(argv[1], mode) == -1) {
>         perror("lchmod");
> 	exit(EXIT_FAILURE);
>     }
> 
>     exit(EXIT_SUCCESS);
> }
> 
> $ touch a 
> $ ln -s a b
> $ ./t_lchmod b 700
> lchmod: Operation not supported
> $ ./t_lchmod /proc/self/fd/0 700
> lchmod: Operation not supported
> ]]
> 
> 
> Thanks,
> 
> Michael
> 
> =====
> 
> 
>>From 56ce64325fa9a9184b820eac908ecc5d53a5154b Mon Sep 17 00:00:00 2001
> From: Bruno Haible <bruno@clisp.org>
> Date: Sun, 10 Jan 2021 05:20:30 +0100
> Subject: [PATCH] chmod.2, lchmod.3: Document lchmod().
> 
> ---
>  man2/chmod.2  | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  man3/lchmod.3 |  1 +
>  2 files changed, 65 insertions(+), 6 deletions(-)
>  create mode 100644 man3/lchmod.3
> 
> diff --git a/man2/chmod.2 b/man2/chmod.2
> index a54aec7..f1709ef 100644
> --- a/man2/chmod.2
> +++ b/man2/chmod.2
> @@ -29,15 +29,16 @@
>  .\"   <michael@cantor.informatik.rwth-aachen.de>: NFS details
>  .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
>  .\"
> -.TH CHMOD 2 2017-09-15 "Linux" "Linux Programmer's Manual"
> +.TH CHMOD 2 2021-01-10 "Linux" "Linux Programmer's Manual"
>  .SH NAME
> -chmod, fchmod, fchmodat \- change permissions of a file
> +chmod, fchmod, lchmod, fchmodat \- change permissions of a file
>  .SH SYNOPSIS
>  .nf
>  .B #include <sys/stat.h>
>  .PP
>  .BI "int chmod(const char *" pathname ", mode_t " mode );
>  .BI "int fchmod(int " fd ", mode_t " mode );
> +.BI "int lchmod(const char *" pathname ", mode_t " mode );
>  .PP
>  .BR "#include <fcntl.h>" "           /* Definition of AT_* constants */"
>  .B #include <sys/stat.h>
> @@ -68,6 +69,12 @@ Feature Test Macro Requirements for glibc (see
>  .\"        || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
>  .fi
>  .PP
> +.BR lchmod ():
> +.nf
> +    Since glibc 2.32:
> +        _DEFAULT_SOURCE
> +.fi
> +.PP
>  .BR fchmodat ():
>  .nf
>      Since glibc 2.10:
> @@ -80,10 +87,12 @@ The
>  .BR chmod ()
>  and
>  .BR fchmod ()
> -system calls change a files mode bits.
> +system calls and the
> +.BR lchmod ()
> +function change a file's mode bits.
>  (The file mode consists of the file permission bits plus the set-user-ID,
>  set-group-ID, and sticky bits.)
> -These system calls differ only in how the file is specified:
> +These functions differ only in how the file is specified:
>  .IP * 2
>  .BR chmod ()
>  changes the mode of the file specified whose pathname is given in
> @@ -93,6 +102,11 @@ which is dereferenced if it is a symbolic link.
>  .BR fchmod ()
>  changes the mode of the file referred to by the open file descriptor
>  .IR fd .
> +.IP *
> +.BR lchmod ()
> +is like
> +.BR chmod (),
> +but does not dereference symbolic links.
>  .PP
>  The new file mode is specified in
>  .IR mode ,
> @@ -220,8 +234,13 @@ can either be 0, or include the following flag:
>  If
>  .I pathname
>  is a symbolic link, do not dereference it:
> -instead operate on the link itself.
> -This flag is not currently implemented.
> +instead operate on the link itself, like
> +.BR lchmod ().
> +(By default,
> +.BR fchmodat ()
> +dereferences symbolic links, like
> +.BR chmod ().)
> +This flag is implemented since glibc 2.32.
>  .PP
>  See
>  .BR openat (2)
> @@ -304,6 +323,17 @@ See above.
>  The same errors that occur for
>  .BR chmod ()
>  can also occur for
> +.BR lchmod ().
> +The following additional errors can occur for
> +.BR lchmod ():
> +.TP
> +.B EOPNOTSUPP
> +.B /proc
> +is not mounted.
> +.PP
> +The same errors that occur for
> +.BR chmod ()
> +can also occur for
>  .BR fchmodat ().
>  The following additional errors can occur for
>  .BR fchmodat ():
> @@ -323,14 +353,31 @@ is relative and
>  is a file descriptor referring to a file other than a directory.
>  .TP
>  .B ENOTSUP
> +(Before glibc 2.32.)
>  .I flags
>  specified
>  .BR AT_SYMLINK_NOFOLLOW ,
>  which is not supported.
> +.TP
> +.B EOPNOTSUPP
> +(Since glibc 2.32.)
> +.I flags
> +specified
> +.BR AT_SYMLINK_NOFOLLOW ,
> +and
> +.B /proc
> +is not mounted.
>  .SH VERSIONS
>  .BR fchmodat ()
>  was added to Linux in kernel 2.6.16;
>  library support was added to glibc in version 2.4.
> +.PP
> +.BR lchmod ()
> +and the handling of
> +.B AT_SYMLINK_NOFOLLOW
> +in
> +.BR fchmodat ()
> +were added in glibc version 2.32.
>  .SH CONFORMING TO
>  .BR chmod (),
>  .BR fchmod ():
> @@ -362,6 +409,17 @@ glibc constructs a pathname based on the symbolic link in
>  that corresponds to the
>  .IR dirfd
>  argument.
> +.SH BUGS
> +.BR lchmod ()
> +and
> +.BR fchmodat ()
> +with
> +.B AT_SYMLINK_NOFOLLOW
> +flag fail with error
> +.B EOPNOTSUPP
> +when the
> +.B /proc
> +file system is not mounted.
>  .SH SEE ALSO
>  .BR chmod (1),
>  .BR chown (2),
> diff --git a/man3/lchmod.3 b/man3/lchmod.3
> new file mode 100644
> index 0000000..92647d2
> --- /dev/null
> +++ b/man3/lchmod.3
> @@ -0,0 +1 @@
> +.so man2/chmod.2
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-01-18 16:12 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-01-10  4:37 [patch] chmod.2, lchmod.3: Document lchmod() Bruno Haible
2021-01-10  7:41 ` Dmitry V. Levin
2021-01-10 10:05   ` Bruno Haible
2021-01-10 17:50     ` Dmitry V. Levin
2021-01-11  8:02     ` Michael Kerrisk (man-pages)
2021-01-18 16:00       ` Michael Kerrisk (man-pages)

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