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+++ This bug was initially created as a clone of Bug #1217236 +++ To test, either have ksh as login shell, or create a test user. Then ssh localhost. Sample session: ---8<--- $ cd /tmp/alan $ cat tst.ksh #!/bin/ksh D=$(date) echo $D > /tmp/alan/tst.dat $ ls tst.ksh $ (ksh /tmp/alan/tst.ksh &) [1] 28190 $ ls tst.ksh ---8<--- 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. ---8<--- 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; sfsync(NIL(Sfio_t*)); while((pid=fork())< 0) _sh_fork(shp,pid,0,0); if(pid==0) { +#endif sh_exec(t->par.partre,flags); +#if 0 shp->st.trapcom[0]=0; sh_done(shp,0); } +#endif } else sh_subshell(shp,t->par.partre,flags,0); ---8<--- 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).
Reported for rawhide, but happens in all non EOL Fedora releases.
This bug appears to have been reported against 'rawhide' during the Fedora 23 development cycle. Changing version to '23'. (As we did not run this process for some time, it could affect also pre-Fedora 23 development cycle bugs. We are very sorry. It will help us with cleanup during Fedora 23 End Of Life. Thank you.) More information and reason for this action is here: https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora23
This bug is a regression of a fix that upstream made: 10-09-21 A bug in the processing of (command&) which created a job in the parent process has been fixed. and exactly the commented-out code was added as the fix (original code also did a backup and restoration of sh.bckpid around sh_exec. So we can't just revert that change.
Fixed in ksh-20120801-28.fc24 ksh-20120801-28.fc23 ksh-20120801-27.fc22 ksh-20120801-27.fc21