| Subject: | failure to check return value of sysseek/truncate/syswrite may lead to false positive |
When writing the PID to the pidfile, Proc::PID::File does not check the
return value of the file functions sysseek, truncate and syswrite. Under
certain conditions, these calls may fail, after which running() will
erroneously return false. As a result, multiple instances of your
program may be active at the same time.
I have attached a suggested patch, considering that "die" is favorable
over mistakenly returning false.
FWIW, I encountered a problem when my /var partition ran out of disk
space. Proc::PID::File then created an empty pid file, leading
subsequent instances to the conclusion that my daemon wasn't running.
Environment:
Proc::Pid::File version 1.24
perl 5.8.8 built for i686-linux
CentOS 4.x on i686, kernel 2.6.9-34.0.1.ELsmp
| Subject: | proc-pid-file.diff |
--- orig/Proc/PID/File.pm 2004-04-08 02:27:25.000000000 +0000
+++ fixed/Proc/PID/File.pm 2006-12-14 15:36:02.000000000 +0000
@@ -109,9 +109,9 @@
}
$self->debug("writing: $$");
- sysseek FH, 0, 0;
- truncate FH, 0;
- syswrite FH, "$$\n", length("$$\n");
+ sysseek FH, 0, 0 or die "sysseek failed: $!";
+ truncate FH, 0 or die "truncate failed: $!";
+ syswrite FH, "$$\n", length("$$\n") or die "syswrite failed: $!";
close(FH) || die qq/Cannot write pid file "$path": $!\n/;
return 0;