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Check ps output to see if file is running, if not start it
This comes in handy if you have daemons/programs that have potential issues and stop/disappear, etc., can be run in cron to ensure that a program remains up no matter what. Be advised though, if a program did core out, you'd likely want to know why (gdb) so use with caution on production machines.

convert ascii string to hex
You can use "decode()" in a similar manner: $ python -c 'print "68656c6c6f".decode("hex")'

convert vdi to vmdk (virtualbox hard disk conversion to vmware hard disk format)
Converts a .vdi file to a .vmdk file for use in a vmware virtual machine. The benefit: using this method actually works. There are others out there that claim to give you a working .vmdk by simply using the qemu-img command alone. Doing that only results in pain for you because the .vmdk file will be created with no errors, but it won't boot either. Be advised that these conversions are very disk-intensive by nature; you are probably dealing with disk images several gigabytes in size. Once finished, the process of using the new .vmdk file is left as an exercise to the reader.

Print number of mb of free ram
This will show the amount of physical RAM that is left unused by the system.

Recursively compare two directories and output their differences on a readable format

Find files and calculate size of result in shell
Find files and calculate size with stat of result in shell

count files by type
displays a list of all file extensions in current directory and how many files there are of each type of extension in ascending order (case insensitive)

Generate an XKCD #936 style 4 word passphrase (fast)
Some snippets posted are slow on big dictionaries, this one is fast.

replace a character/word/string in a file using vim
Replace all ocurrences in the file. The g option is to replace more than one occurrence in the same line. Whitout the g option, it only replace the first occurrence in the line.

List all active access_logs for currently running Apache or Lighttpd process
Ever logged into a *nix box and needed to know which webserver is running and where all the current access_log files are? Run this one liner to find out. Works for Apache or Lighttpd as long as CustomLog name is somewhat standard. HINT: works great as input into for loop, like this: $ for i in `lsof -p $(netstat -ltpn|awk '$4 ~ /:80$/ {print substr($7,1,index($7,"/")-1)}')| awk '$9 ~ /access.log$/ {print $9| "sort -u"}'` ; do echo $i; done Very useful for triage on unfamiliar servers!


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