Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site umcp-cs.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!umcp-cs!chris From: chris@umcp-cs.UUCP (Chris Torek) Newsgroups: net.unix-wizards Subject: Re: Question on how to implement exclusive scheduling Message-ID: <373@umcp-cs.UUCP> Date: Tue, 16-Oct-84 22:31:04 EDT Article-I.D.: umcp-cs.373 Posted: Tue Oct 16 22:31:04 1984 Date-Received: Thu, 18-Oct-84 06:43:49 EDT References: <620@trwspp.UUCP> <154@desint.UUCP> Organization: U of Maryland, Computer Science Dept., College Park, MD Lines: 26 Note, however, that implementing arbitrary mandatory locking is not a good idea as anyone can then write something like this: #includemain() { int fd, i; for (i = 0; i < 31; i++) (void) signal(i, SIG_IGN); fd = open("/etc/passwd", 0); lockf(fd, -1); /* lock it to EOF */ pause(); /* or, for(;;); is even more malicious */ } If there are no system administrators already logged in you may have to halt the machine from the console. There are numerous ways around this, the easiest probably being to use advisory locks rather than mandatory locks. -- (This mind accidently left blank.) In-Real-Life: Chris Torek, Univ of MD Comp Sci (301) 454-7690 UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris CSNet: chris@umcp-cs ARPA: chris@maryland