Bug 1217236 - ksh misbehavior if login shell "( cmd & )" does nothing and no error reported
Summary: ksh misbehavior if login shell "( cmd & )" does nothing and no error reported
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: ksh
Version: 6.6
Hardware: All
OS: All
Target Milestone: rc
: ---
Assignee: Michal Hlavinka
QA Contact: Martin Kyral
Milan Navratil
Depends On:
Blocks: 1075802 1172231 1217237 1217238 1254457 1269889
TreeView+ depends on / blocked
Reported: 2015-04-29 20:28 UTC by Paulo Andrade
Modified: 2019-10-10 09:47 UTC (History)
3 users (show)

Fixed In Version: ksh-20120801-32.el6
Doc Type: Bug Fix
Doc Text:
KornShell no longer omits a background process in a command list when forking Due to a bug in KornShell (ksh), forking a background process in a command list could previously omit that process completely. The source code that handles forking sub-processes has been modified, and a background process in a command list is now executed as expected.
Clone Of:
: 1217237 1217238 (view as bug list)
Last Closed: 2016-05-11 00:45:47 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2016:0932 0 normal SHIPPED_LIVE ksh bug fix update 2016-05-10 22:54:18 UTC

Description Paulo Andrade 2015-04-29 20:28:56 UTC
To test, either have ksh as login shell, or create a test user.
Then ssh localhost.

Sample session:

$ cd /tmp/alan
$ cat tst.ksh

echo $D > /tmp/alan/tst.dat

$ ls
$ (ksh /tmp/alan/tst.ksh &)
[1]	28190
$ ls

This happens due to a double fork, once for "( cmd )" and
then the first fork forks again due to the "&", but, just
when the child branches, it receives a SIGHUP and
immediately exits.

I tested a quick&dirty patch, that basically reverts to
rhel5 ksh behavior, and there are no regressions in the
test cases.

diff -up ksh-20120801/src/cmd/ksh93/sh/xec.c.orig ksh-20120801/src/cmd/ksh93/sh/xec.c
--- ksh-20120801/src/cmd/ksh93/sh/xec.c.orig	2015-04-28 16:55:25.521818636 -0300
+++ ksh-20120801/src/cmd/ksh93/sh/xec.c	2015-04-28 16:56:34.037753565 -0300
@@ -2059,16 +2059,20 @@ int sh_exec(register const Shnode_t *t,
 			else if(((type=t->par.partre->tre.tretyp)&FAMP) && ((type&COMMSK)==TFORK))
+#if 0
 				pid_t	pid;
 				while((pid=fork())< 0)
+#if 0

I also asked upstream, see http://lists.research.att.com/pipermail/ast-users/2015q2/004754.html
but actually, there is a bad comment there, about crashes if
running it as "( cmd ) &". Likely it was due to the way I was
debugging it.

Note that if one has bash as login shell, then starts, or exec
ksh, or even if has ksh as login shell, and first exec ksh,
it will work, because then SIGHUP will be blocked in the
"orphan" process (orphan due to double fork).

Comment 9 errata-xmlrpc 2016-05-11 00:45:47 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.


Note You need to log in before you can comment on or make changes to this bug.