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More Deep Discovery on your Linux Server With /proc

Jan 19, 2011, 18:34 (0 Talkback[s])
(Other stories by Juliet Kemp)

"Linux's amazing and powerful pseudo-filesytem proc isn't just for peering into a running kernel. Juliet Kemp shows how Linux admins can also change kernel parameters on the fly.

"Last month I looked at some of the interesting data you can get out of /proc/. But /proc isn't just for getting information out of the system and into convenient text form. You can also use it to put information into the system, and thereby change it. The sys/ directory, which is where kernel variable information is kept, is where most of the things you might want to alter live. Changes made here will take effect immediately; no need to reboot. A real boon for working sysadmins! Note that you'll need appropriate (root) privileges to change these values. See here for a discussion of using sudo with pipes.

"Networking changes

"/proc/sys/net/ipv4/ contains a bunch of networking values to try playing around with.

"/proc/sys/net/ipv4/tcp_keepalive_time sets how long (in seconds) it takes the TCP keepalive routines to send the first keepalive probe. A keepalive message simply detects whether the other side of the connection is still there; if not, it drops the connection. However, the default is 7200 seconds (2 hours), which is probably after your session would have timed out itself. If you want something quicker than that, you can change this value to send a keepalive sooner (and thus drop the session sooner if the other side has gone away). Setting it to 120 seconds would start sending keepalives after two minutes."

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