STRAY neuron

Little know seq (sequence) utility is a great way to loop on a range of numbers in Linux. It came in very handy today and will hopefully stick in my brain in the future.

for i in `seq 1 10`
do
..
done

I discovered a large gap in my bash kung fun today - I had no idea how to loop on lines of data in a file.

It turns out that “while data” pulls off this trick quite nicely:


while read myline
  do $myline
done < inputfile


I was sick of typing in username/password for each login (I’m currently working on XP, deploying to a Linux-only env), so I finally went through the pain of following the steps here and set up PuTTY/Peagant public key authentication.

It was a relatively painless setup process, but here are a couple of things to keep in mind when going through it:

• PuTTY is a pain to update/navigate as you have to remember to load/save during each setting update
• You can “pre-enter” your remote username by setting “username@hostname” as the hostname
• authorized_keys file on the remote box should have a mask of 600
• putty.exe -load “session_name” allows you to create PuTTY shorcuts for each of your connections

Would you like to create a lively, “top”-like output from some of the monitoring commands in your toolbelt?

“watch” can be of help here, as it can poll your command every X seconds and render its output to full screen.

Try “watch -n1 date” for a demo.

NAME
watch - execute a program periodically, showing output fullscreen

SYNOPSIS
watch [-dhv] [-n ] [–differences[=cumulative]] [–help]
[–interval=] [–version]

I’m administering a mix of Red Hat and Debian boxes, so this tip from bschmitz comes in handy…

cat /proc/version

Simple thing to do…had to look it up…

kill -HUP `cat /var/run/sshd.pid`

I stumbled onto this while troubleshooting Putty disconnects on XP…gotta love FAQs w/ attitude.

A.7.12 When I cat a binary file, I get ‘PuTTYPuTTYPuTTY’ on my command line.

Don’t do that, then.

This is designed behaviour; when PuTTY receives the character Control-E from the remote server, it interprets it as a request to identify itself, and so it sends back the string ‘PuTTY’ as if that string had been entered at the keyboard. Control-E should only be sent by programs that are prepared to deal with the response. Writing a binary file to your terminal is likely to output many Control-E characters, and cause this behaviour. Don’t do it. It’s a bad plan.

Check out Jeremy Mates’ reallykill script if you need to effectively kill a processes with a preference for graceful shutdown.

Bookmarking this…since I’m having lock problems with BerkeleyDB…

$ svnadmin create –fs-type fsfs /path/to/new/repository
$ svnadmin dump /path/to/repository | svnadmin load /path/to/new/repository

UPDATE (12/26/2006): I ended up pulling the trigger on the BerkeleyDB->FSFS conversion as I was getting absolutely sick of running the “svnadmin recover” and “db_recover” scripts. Conversion was painless - here’s the “productionalized” list of steps I followed:

1. Shut down svnserve, Apache, and anything else that might be accessing the repository.
2. svnadmin dump /path/to/repository > dumpfile.txt
3. mv /path/to/repository /path/to/saved-old-repository
5. svnadmin create –fs-type fsfs /path/to/repository
6. svnadmin load /path/to/repository < dumpfile.txt
7. Copy over hook scripts, etc, from the old repository to the new one.
8. Restart svnserve, Apache, etc.

Useful tip by Todd Huss - test your cron scripts using the env -i somescript.sh command