If I could only take two pieces of software with me onto a deserted island, the first would be Vim, the second would be Screen. Screen provides two very important features that make my life quite a bit easier.

1. Persistence. If the network has an error, or I just happen to click the silly little x on my terminal window, then all I have to do is ssh back into the server and restart screen (screen -r). It will be like I never left. This means that I don’t have to worry about running everything with a nohup, and if I start a job at work I can go home and reconnect (screen -Dr) to my terminal session in order to continue monitoring the job.
2. Multiple windows. Ssh into the server, start up screen, start a job in that shell, type ‘Ctrl-a c’, and voila, a new shell in a new window. Now I can go and adjust the size and position of the windows. For instance, let’s say that I need to tail five different log files. I can start up five windows, resize and position them all on the screen, and then I’m monitoring all those files in one terminal session. I can switch back and forth between the windows by typing ‘Ctrl-a #’ where # is the number of the window, ‘Ctrl-a n’ for next, ‘Ctrl-a p’ for previous, or ‘Ctrl-a “‘ to get a list of all the windows that you can arrow up or down through. You can also rename the window you are in by typing ‘Ctrl-a A’.

Unfortunately, screen sucks straight out of the box. I recommend creating a .screenrc with these lines at a minimum:

startup_message off
shell bash

termcapinfo xterm "ks=E[?1lE:kuE[A:kd=E[B:kl=E[D:kr=E[C:kh=E[5~:kH=E[F"

caption always "%{= bb}%{+b w}%n %h %=%t %c"
hardstatus alwayslastline "%{-b gk}%-w%{+b kg}%50>%n %t%{-b gk}%+w%<"

" screen starts at window 0. These two lines make the first window 1, and
" binds 0 to window 10.
bind c screen 1
bind 0 select 10

After starting screen you should now have two lines at the bottom of your screen. The first should be blue and have the window number, name, and system time. The second should be green and have a listing of all the current windows and their names. I prefer a dark background and these colors work really well on top of black. You should review the screen manpage for more things that you can add to those status lines. One of my favorites is %l which displays the current load on the system.

Another thing that you can do with screen is create custom screenrc files for different situations. I have several that I use which automatically open certain windows for me. For instance, if I “cp .screenrc .mysqlscreenrc” and then add the following lines to the bottom of .mysqlscreenrc:

screen -t "database 1"   1 mysql -h hostname -u username -ppassword data1
screen -t "database 2"   2 mysql -h hostname -u username -ppassword data2
screen -t "localhost"    3 bash

Then, add this alias “alias mysqlscreen=’screen -S mysql -c ~/.mysqlscreenrc’”. Now all you have to do is type mysqlscreen when you log in, and it will automatically open three windows for you. Two of them will open up mysql monitor sessions, and the third will open up a shell. The -S part of the screen command names the screen session. That way if you become disconnected then a ’screen -ls’ will be more meaningful, and it will be easier to know which session is which when you do your ’screen -r’.

This entry was posted on Monday, May 28th, 2007 at 7:47 am and is filed under Administration. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.