I expect that you are picking up the PID of the "grep".

To check whether is happening, try this quick test.

ps -ef | grep "grep"

ps -ef | grep "/var/lib/dpkg/lock" | grep -v "grep" | awk '{print $2}'

at

ps -ef | grep "/var/lib/dpkg/lock" | awk '{print $2}'

kill 3058

bash: kill: (3058) - Aucun processus de ce type
(no such process)

i think nothing...

ps -ef | grep "/var/lib/dpkg/lock" | awk '{print $8}'

gives me...

...grep

-----Post Update-----

nope.

i expect to find out which software is monopolizing my lock file...

i guess that it is the automatic updates process from gnome, but i would like to end it and manually install another software from the console using aptitude.

any clue ?