Pedro Zorzenon

    as per http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=242638
    Noted use of _XOPEN_SOURCE to get macros <sytdlib.h>
    as for wait(2).

mtk
    Changed name of argument from 'string' to 'command' (like POSIX).

    Noted that glibc does nowadays explicitly check for the existence
    of the shell if 'command' is NULL, rather than the older behaviour
    of assuming the shell exists and always returning 1 if
    'command' is NULL.

    Other wording and formatting clean-ups.

1 files changed, 40 insertions, 23 deletions

diff --git a/man3/system.3 b/man3/system.3
index add7bc6d..795c53ff 100644
--- a/man3/system.3
+++ b/man3/system.3
@@ -23,23 +23,24 @@
 .\" Modified Sat Jul 24 17:51:15 1993 by Rik Faith (faith@cs.unc.edu)
 .\" Modified 11 May 1998 by Joseph S. Myers (jsm28@cam.ac.uk)
 .\" Modified 14 May 2001, 23 Sep 2001 by aeb
+.\" 2004-12-20, mtk
 .\"
-.TH SYSTEM 3  2001-09-23 "" "Linux Programmer's Manual"
+.TH SYSTEM 3  2004-12-20 "" "Linux Programmer's Manual"
 .SH NAME
 system \- execute a shell command
 .SH SYNOPSIS
 .nf
 .B #include <stdlib.h>
 .sp
-.BI "int system(const char *" "string" );
+.BI "int system(const char *" "command" );
 .fi
 .SH DESCRIPTION
-.B system()
+.BR system ()
 executes a command specified in
-.I string
+.I command
 by calling
 .BR "/bin/sh -c"
-.IR string ,
+.IR command ,
 and returns after the command has been completed.
 During execution of the command,
 .B SIGCHLD
@@ -57,26 +58,34 @@ specified in
 Thus, the exit code of the command will be
 .IR WEXITSTATUS(status) .
 In case
-.B "/bin/sh"
+.I "/bin/sh"
 could not be executed, the exit status will be that of
 a command that does
 .IR exit(127) .
 .PP
 If the value of
-.I string
+.I command
 is 
 .BR NULL ,
-.B system()
+.BR system ()
 returns nonzero if the shell is available, and zero if not.
 .PP
-.B system()
+.BR system ()
 does not affect the wait status of any other children.
 .SH "CONFORMING TO"
 ANSI C, POSIX.2, BSD 4.3
 .SH NOTES
 .PP
+If the
+.B _XOPEN_SOURCE
+feature test macro is defined, then the macros described in
+.BR wait (2)
+.RB ( WEXITSTATUS() ,
+etc.) are made available when including
+.IR <stdlib.h> . 
+.PP
 As mentioned,
-.B system()
+.BR system ()
 ignores SIGINT and SIGQUIT.  This may make programs that call it
 from a loop uninterruptable, unless they take care themselves
 to check the exit status of the child. E.g.
@@ -93,33 +102,41 @@ to check the exit status of the child. E.g.
 .fi
 .PP
 Do not use
-.B system()
-from a program with suid or sgid privileges, because strange values for
-some environment variables might be used to subvert system integrity.
+.BR system ()
+from a program with set-UID or set-GID privileges,
+because strange values for some environment variables
+might be used to subvert system integrity.
 Use the
 .BR exec (3)
 family of functions instead, but not
 .BR execlp (3)
 or
 .BR execvp (3).
-.B system()
-will not, in fact, work properly from programs with suid or sgid
+.BR system ()
+will not, in fact, work properly from programs with set-UID or set-GID
 privileges on systems on which
-.B /bin/sh
+.I /bin/sh
 is bash version 2, since bash 2 drops privileges on startup.
 (Debian uses a modified bash which does not do this when invoked as
 .BR sh .)
 .PP
-The check for the availability of
-.B /bin/sh
-is not actually performed; it is always assumed to be available.  ISO
-C specifies the check, but POSIX.2 specifies that the return shall
-always be non-zero, since a system without the shell is not
-conforming, and it is this that is implemented.
+In versions of glibc before 2.1.3, the check for the availability of
+.I /bin/sh
+was not actually performed if
+.I command
+was NULL; instead it was always assumed to be available, and
+.BR system ()
+always returned 1 in this case.
+Since glibc 2.1.3, this check is performed because, even though
+POSIX.1-2001 requires a conforming implementation to provide
+a shell, that shell may not be available or executable if
+the calling program has previously called
+.BR chroot (2)
+(which is not specified by POSIX.1-2001).
 .PP
 It is possible for the shell command to return 127, so that code is not
 a sure indication that the
-.B execve()
+.BR execve ()
 call failed.
 .SH "SEE ALSO"
 .BR sh (1),