My Nagios Checks (for Linux)

What's here:

• check_mem checks memory usage with warning and critical levels in percentages. The check reports all the usual numbers and some lesser known values: reclaimable slab, this is memory used by the kernel that may be reclaimed under memory pressure, I got it get quite big when rsyncing 1+ million files, use slabtop to find out what's in your slab; and committed memory, this is the sum of all memory allocated by (promised to) processes, they may not use it all, but they might want to use it at some point. Plot the performance data with a lineformat like rest,data=AREA;sReclaimable,data=AREA,STACK;buffers,data=AREA,STACK;cached,data=AREA,STACK. The check uses /proc/meminfo.
• check_mount checks space used as a percentage of the usable space (total space excluding the reserved-for-root blocks). I prefer this to checking the inverse, which Nagios' check_disk does. This check also provides a more useful status report. The check uses stat -f.
• check_io doesn't check anything but returns bytes/iops read/written for a block device since the last invocation. /sys/block/*/stat is used as the source.
• check_if also doesn't check anything, it returns bytes received and sent for an interface since the last invocation. /sys/class/net/*/statistics/* is used as the source.
• check_fpm checks if a PHP-FPM pool is responsive. The number of idle and active processes and the queue (maximum) length are reported. It requires xmlstarlet and the cgi-fcgi binary (package fcgi on EPEL, libfcgi0ldbl on Debian).
• check_redis checks if Redis is alive and reports its statistics, some of them (hits, misses, etc.) averaged since the last invocation (to hits per second, misses per second, etc.).
• check_apc checks PHP APC available memory, hit ratio, expunges, etc. Make this script available and point the check to it: <?php foreach(apc_sma_info(true) + apc_cache_info('', true) as $k => $v) { echo "$k=$v\n"; }. Depends on curl.
• check_ebs_snapshot checks whether an Amazon EBS volume has a recent snapshot. Requires Boto and assumes AWS credentials are set through its configuration.
• check_backup_s3 checks if a location on S3 contains a timestamped backup, and optionally its age and size. Same dependency on Boto.
• check_rds_storage checks the free storage for a given RDS instance. Same dependency on Boto.
• check_urls checks all given URLs. Reports URLs as down (network/http errors and empty responses), timeout (response took longer than 5 seconds), aberrant (response size is less than 25% of previous one), or up. Depends on curl.

All of the checks require bash and bc.