Clarify description of chmod() and fchmod().

Add further detail on S_ISUID, S_ISGID, and S_ISVTX permissions.
Reformat list of permissions bits.

man2/chmod.2

@@ -28,7 +28,7 @@
 .\"   <michael@cantor.informatik.rwth-aachen.de>: NFS details
 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
 .\"
-.TH CHMOD 2 2007-07-26 "Linux" "Linux Programmer's Manual"
+.TH CHMOD 2 2008-05-26 "Linux" "Linux Programmer's Manual"
 .SH NAME
 chmod, fchmod \- change permissions of a file
 .SH SYNOPSIS
@@ -46,54 +46,68 @@ Feature Test Macro Requirements for glibc (see
 .BR fchmod ():
 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
 .SH DESCRIPTION
-.\" FIXME . The description here could be improved.
+These system calls change the permissions of a file.
-The mode of the file given by
+They differ only in how the file is specified:
-.I path
+.IP * 2
-or referenced by
+.BR chmod ()
-.I fd
+changes the permissions of the file specified whose pathname is given in
-is changed.
+.IR path ,
-
+which is dereferenced if it is a symbolic link.
-Modes are specified by
+.IP *
-.I or'ing
+.BR fchmod ()
-the following:
+changes the permissions of the file referred to by the open file descriptor
-.RS
+.IR fd .
-.TP 1.0i
+.PP
-.B S_ISUID
+The new file permissions are specified in
-04000 set user ID on execution
+.IR mode ,
+which is a bit mask created by ORing together zero or
+more of the following:
+.TP 18
+.BR S_ISUID "  (04000)"
+set-user-ID (set process effective user ID on
+.BR execve (2))
 .TP
-.B S_ISGID
+.BR S_ISGID "  (02000)"
-02000 set group ID on execution
+set-group-ID (set process effective group ID on
+.BR execve (2);
+mandatory locking, as described in
+.BR fcntl (2);
+take a new file's group from parent directory, as described in
+.BR chown (2)
+and
+.BR mkdir (2))
 .TP
-.B S_ISVTX
+.BR S_ISVTX "  (01000)"
-01000 sticky bit
+sticky bit (restricted deletion flag, as described in
+.BR unlink (2))
 .TP
-.B S_IRUSR
+.BR S_IRUSR "  (00400)"
-00400 read by owner
+read by owner
 .TP
-.B S_IWUSR
+.BR S_IWUSR "  (00200)"
-00200 write by owner
+write by owner
 .TP
-.B S_IXUSR
+.BR S_IXUSR "  (00100)"
-00100 execute/search by owner
+execute/search by owner ("search" applies for directories,
+and means that entries within the directory can be accessed)
 .TP
-.B S_IRGRP
+.BR S_IRGRP "  (00040)"
-00040 read by group
+read by group
 .TP
-.B S_IWGRP
+.BR S_IWGRP "  (00020)"
-00020 write by group
+write by group
 .TP
-.B S_IXGRP
+.BR S_IXGRP "  (00010)"
-00010 execute/search by group
+execute/search by group
 .TP
-.B S_IROTH
+.BR S_IROTH "  (00004)"
-00004 read by others
+read by others
 .TP
-.B S_IWOTH
+.BR S_IWOTH "  (00002)"
-00002 write by others
+write by others
 .TP
-.B S_IXOTH
+.BR S_IXOTH "  (00001)"
-00001 execute/search by others
+execute/search by others
-.RE
 .PP
 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