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From: eggert@twinsun.com (Paul Eggert)
Newsgroups: comp.unix.shell
Subject: SCCS and RCS over NFS (was: Creating a lock file in sh?)
Message-ID: <1991Apr20.020506.8656@twinsun.com>
Date: 20 Apr 91 02:05:06 GMT
References: <PABLO.91Apr17110430@tofu-hut.csd.sgi.com> <1991Apr17.201931.14536@odin.corp.sgi.com> <784@necssd.NEC.COM> <1991Apr19.201517.3679@odin.corp.sgi.com>
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rhartman@thestepchild.sgi.com (Robert Hartman) writes:

>BTW, does this imply that SCCS and RCS can also fail over NFS?
>I'm not aware of them using the NFS lock manager!

I don't know about SCCS, but RCS 5.5 uses a slightly different
technique.  The lock file never exists in writable form, avoiding the
NFS protocol bug that Jonathan Kamens described.  A similar method can
be used in the shell.  For example (Bourne shell):

	if (umask 777;  echo >lock)
	then
		Perform whatever operation required locking.
		rm -f lock
	else
		Report that you could not obtain the lock.
	fi