Archives for 17 May,2009

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Using the free command gives output something like this (-m just tells free to output in megabytes):

free -m
total used free shared buffers cached
Mem: 2013 1996 17 0 27 1381
-/+ buffers/cache: 588 1425
Swap: 956 0 956

This is useful but annoying as it doesn’t show you how much memory is actually free. Files that are used are kept in the ram (referred to as caching). If the memory is needed it is simply overwritten, however if the file is used again it is already in the memory which saves time.

I wrote a quick little bash line to get the actually memory in use or the actual memory free. I use grep to select the right line from the output of free, and then use awk to do the string manipulation and math.

Memory in use

free -m | grep Mem | awk ‘{x=$3-$7; print x}’

Memory free

free -m | grep Mem | awk ‘{x=$2-($3-$7); print x}’

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apt – no public key error

If you add a new repository to apt (/etc/apt/sources.list) you may get the following error when running ‘sudo apt-get update’:

Reading package lists… Done
W: There is no public key available for the following key IDs:
W: You may want to run apt-get update to correct these problems

As you probably already guessed, running ‘sudo apt-get update’ will result in exactly the same problem. This is because the new repository’s key needs to verified. This is done by the following:

gpg –keyserver –recv [Key]
gpg –export [Key] | sudo apt-key add –

replace [Key] with the key you want to add

This can also be made slightly easier by using a bash variable:

gpg –keyserver –recv $1
gpg –export $1 | sudo apt-key add –

replace [Key] with the key you want to add

or as a bash script:

gpg –keyserver –recv $1
gpg –export $1 | sudo apt-key add –

ran by the following:

./key [key]

replace [Key] with the key you want to add
which then you could place in /bin so you could simply run

Script can be downloaded here

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