Month: November 2010

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Parallel SSH

Parallel SSH is a useful tool designed to run a command on multiple servers in parallel. An advantage of PSSH over some alternatives (like DSH) is the manner outputs are stored: all outputs are sent to a folder containing an output file per server.

Using PSSH

First create your servers list, using the syntax host:port user :

vi /tmp/hosts_list.txt
server1
server2
server3:2222 foobar

Then create two directories: one for standard outputs, the second for error outputs.

mkdir /tmp/output
mkdir /tmp/error

Then execute your command:

parallel-ssh -h /tmp/hosts_list.txt -o /tmp/output/ -e /tmp/error/ uptime

Further Reading and sources

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Make a file immutable

Native linux partition format (like ext2/3/4) have a pretty cool functionality: file attribute. Theses attributes give you some control on how the kernel treat a particular file. The command chattr and lsattr allow you to change and check theses attributes.

One attribute that can be a life saver for system administrator is the ‘immutable’ one. When flagged ‘immutable’ no one, not even root, can change a file. This allow you to prevent any accidental modification. For example let say we want to prevent any change on the /etc/shadow file:

# chattr +i /etc/shadow

When modification are required, we simply remove the flag:

# chattr -i /etc/shadow

There is a lot of other attributes to play with. Check chattr man page for more detail on them.