When I first wrote about DMon, I pointed out that version 0.3 could be already installed from our APT repository, which hosts flavours for i386, amd64 and armel. Five weeks have passed and I feel like I have to write a status update now that 0.3.7 is out. It is not a big version number change because DMon behaves essentially as in 0.3, but a number of new features were added and bugs fixed.

Let’s see which juicy bits are available on top of the features it already had:

• Additional groups can now be specified using the -u and -U options. As a side effect of their extended syntax, options -g and -G were removed as they are no longer needed.
• Setting of resource usage limits is now supported with the -r. This uses setrlimit(2) under the hood.
• DMon can now wait for some time before re-running commands by specifying time intervals with the -i option. Think about it as a poor man’s recurrent job scheduler.
• Environment variables can now be manipulated (including deletion) by means of the -E option.
• All commands (dmon, dlog, dslog) can now be built as a single multicall binary. This saves disk space and some kilobytes of memory, which is interestinhg for embedded environments.
• Tools now honor the DMON_OPTIONS, DLOG_OPTIONS and DSLOG_OPTIONS; environment variables. When defined, they will be interpreted as additional command line arguments. Actual command line arguments take precedence, so values given in environment variablels can still be overriden.
• A small libnofork.so library is included, which overrides the system-provided fork(2) and daemon(3) functions in such a way that the library can be preloaded (dmon -E LD_PRELOAD=libnofork.so ....) to make programs not to fork. Very useful for applications which create new daemon processes inconditionally so they can be properly monitored. This is tested only under GNU/Linux with glibc at the moment, use with care!

Apart from new features, a couple of bugs related to error handling were fixed, for better reliability.

Last but not least, I would like to thank my friend Andrés J. Díaz who is using DMon and provided feedback and ideas for some of those new features.

Happy monitoring!