.lock files

[Rob Bernardo]

In article <19163 at adm.BRL.MIL> SIMSN%NUSDISCS.BITNET at cunyvm.cuny.edu writes:
+
+
+ -rw-rw----   1 chuase   mail           5 Apr 18 18:06 chuase.lock
+ -rw-rw----   1 root     mail          96 Apr 18 17:57 root
+ -rw-rw----   1 yanll    mail           5 Apr 18 17:29 yanll.lock
+ -rw-rw----   1 simsn    mail           5 Apr 18 17:20 simsn.lock
+ drwxrwxr-x   2 root     mail          48 Apr 18 17:16 :saved
+ -rw-rw----   1 repo     mail           1 Apr 18 17:06 repo.lock
+ -rw-rw----   1 tankuany mail           3 Apr 18 16:02 tankuany.lock
+ -rw-rw----   1 lawtongl mail           5 Apr 18 16:01 lawtongl.lock
+ -rw-rw----   1 tansiewb mail         581 Apr 18 15:58 tansiewb
+
+
+ $ cat simsn.lock
+ 29006 $
+
+
+ The above is a portion of my /usr/mail and the contents of one of
+ the lock files is also shown. Other lock files have different numbers.
+
+ Can anyone please explain .lock files? We have a AT&T 3B4000/15 running
+ Sys V 3.1.1 and we use /bin/mail and /usr/bin/mailx

The .lock files are a convention used by programs that write to mailboxes
as a way of preventing two processes from writing to the same mailbox
at the same time. Some mail program with the current process id in the
lock file. This way another process can tell if the lock file is
obsolete or not (by checking to see if there is a process still
running with that process id.)

Isn't it odd that there should be so many lock files in that directory 
just when you did your ls -l? Not really. There is a bug in mailx. 
If invoked with the -e flag (often done in /etc/profile to report to a 
user who is logging in on the presence of mail) it creates the lock 
file but doesn't remove it. Such an obsolete lock file doesn't bother
mailx as it removes an obsolete lock file when it encounters one,
but other mail programs might work differently. I have seen
mail programs that deal with lock files in the following ways:

	1. wait for the lock file to be removed
	2. wait and try again and then remove the lock file
	   after so many tries under the assumption that
	   the lock file is obsolete
	3. wait and try again and then give up after so many tries

I am not an expert, but I would recommend that "mail -e" be used
in place of "mailx -e" in /etc/profile so that there is no interference
with any other mail programs you might have or acquire in the future.
-- 
Rob Bernardo, Pacific Bell UNIX/C Reusable Code Library
Email:     ...![backbone]!pacbell!pbhyf!rob   OR  rob at pbhyf.PacBell.COM
Office:    (415) 823-2417  Room 4E850O San Ramon Valley Administrative Center
Residence: (415) 827-4301  R Bar JB, Concord, California