Enormous utmp since mpsafetty

Robert Watson rwatson at FreeBSD.org
Wed Aug 27 11:50:18 UTC 2008

On Wed, 27 Aug 2008, Ollivier Robert wrote:

> According to Gary Jennejohn:
>> There are many more pseudo-ttys in /etc/ttys now.  AFAIK utmp allocates an 
>> entry for every one of them at startup.
> utmp concepts are ancient.  It is indexed by the tty/pty number so can grow 
> rather large but it should be a sparse one too.  I remember talks about 
> replacing it with something a bit more modern.  Backward compatibility is 
> assured through login(3) although it would break programs digging in the 
> utmp file itself.  SVR4 had utmp/utmpx and setutline/getutline BTW...

Right -- utmp growing to 256K would be an excellent example of utmp format 
inefficiency.  On the other hand, utmp growing to 998M is probably an example 
of a bug rather than an inefficient design.  freefall.FreeBSD.org, a 
relatively busy shell box, has a utmp of around 5k, so common use doesn't 
generally exercise that inefficiency...

Robert N M Watson
Computer Laboratory
University of Cambridge

> cf. sessreg(1)
>       System  V has a better interface to utmp than BSD; it dynamically allo-
>       cates entries in the file, instead of writing them at  fixed positions
>       indexed by position in /etc/ttys.
> -- 
> Ollivier ROBERT -=- FreeBSD: The Power to Serve! -=- roberto at keltia.freenix.fr
> Darwin sidhe.keltia.net Version 9.2.0: Tue Feb  5 16:13:22 PST 2008; i386
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