tech.superhappykittymeow.com

via Paul (lovepig.org):

This one-liner is quite effective when tossed into a file and run as a cronjob once per minute. Any IP with more than 100 concurrent connections — which, quite honestly, is far more than any one IP should ever have on a standard webserver — will be blocked via iptables. This script as a cronjob is extremely effective dealing with small-to-midsize DDoSes (too much traffic for Apache/whatever service to handle, but not saturating the pipe).

…for a list of domains, without digging through the database!

'domains', of course, is a text file with a list of domains hosted on the server. Can be populated in whatever way you need. Easily plugged into other Plesk utilities (such as changing Plesk FTP passwords).

To combine two (or more) text files as individual columns in the same file, such as:

file1:

file2:

into:

rather than using an ugly combination of sed and awk, you can use the `paste' command:

You can use the `sort' utility to sort not only on the first field, but also an arbitrary column. Take this output from ps:

This can be sorted by the SZ column, column 9, as such:

The -k switch tells sort to sort based on a key, which we specify as 9n (column 9, numeric). Much easier to review the output.

Runs in the foreground a simple, single-threaded web server on port 8000 as the current user. Logging is to stdout/stderr, and a ctrl-c will stop the server. Great for temporarily sharing a directory.

Great for command-line logging into sites to pull content for whatever reason.

Of course, you'll have to look at the source for the target location's login page to see what variables it wants. I use it to grab a single Cacti-generated graph that is normally password protected, but I want to include a single graph on another site, so I cron'd a script to run a line similar to the above to log in and save it locally.

from command-line-fu

Spot DDoS's and the like quickly:

Thanks Geoff!

If you add an entry to crontab that is an interval, such as */3 (every 3 minutes), you can verify that it runs at the specified interval with a bit of awk:

This essentially checks to see that the minute field of the timestamp is divisible by three — the interval. It'll also run at 00 after the hour, not divisible by three, but expected.

Cron can "run late" at times due to high load situations, so if there are any irregularities in your intervals, you may wish to investigate deeper, looking for expensive processes that are chewing up precious cron time.

Ever wish you knew what Apache was working on at any given moment, but kicking yourself because you forgot to enable a server-status directive? This snippet will help you diagnose timeouts and long-running scripts (for bad coders like myself):

Set bash's internal field seperator to an enter instead of a space, so grep (or whatever) doesn't freak out:

Find total sizes of files in all those logs directories

To find files that do NOT contain a specific string you can do the following:

will list all files named ifcfg-eth0:* that do not contain the string ONBOOT.

You can script this up as such:

to add the required ONBOOT=yes line to the config.

What's eating up all your disk space?

The only caveat is that you have to know the table that comes after the one you're trying to extract.  It's alphabetical, if you can get a list of tables, otherwise a quick search of the SQL file will get that info for you.

Check to see if a perl module is installed:

(no output == success)

Check perl module versions:

Find out where a perl module is installed (docs, sources, etc):

Find all non-Red Hat-supplied packages:

Handy for diagnosing issues where things seem a little "off".

The last number is the CPU the process is currently waiting on.  Quite useful when used in conjunction with `top', as hitting the number 1 while in interactive mode will display the per-CPU usage.  Helpful to find iowait.