Latest Updates: bsd

  • Using grep to Exclude Lines Containing Certain Characters/Text

    04:37 on January 10, 2010 | 0 Comments Tweet This! | Digg This!
    Tags: bsd, ,

    I like to watch Apache log files using tail -f but they often get filled up with data I don’t want/need to see – like, when I access the web site.

    grep is a great tool to search for certain information in text files – but it can also exclude certain pieces of information which can be equally as useful.

    So, for example, if I want to watch a log file using tail -f, but exclude any information relating to the IP address “192.168.1.101″ then we can use the grep -v switch:

    tail -f access.log | grep -v "192.168.1.101"

    What this will do is show everything, apart from a line with that IP address in.

    Of course, this works with any other command with text being piped into grep:

    cat file.txt | grep -v "heh"

    This would output the contents of file.txt but remove any lines with “heh” in them.

    You can find out more about the various grep options in it’s man page (man grep from the command line)

     

  • Kill a GNU Screen Session from the Command Line

    17:48 on January 4, 2010 | 0 Comments Tweet This! | Digg This!
    Tags: bsd, ,

    This article is about GNU Screen – you can read about GNU Screen here: http://www.gnu.org/software/screen/

    There may be times when you have multiple, or even a single, screen session which you want to kill without attaching to it and ending it as you normally would.

    You can kill a screen session using the session ID or the name (if the name is unique enough).

    Warning: Both ways end all processes within the screen session, so if you have any open files/applications, make sure you don’t need/want them – they’ll be kill’d along with the session.

    Killing by session ID

    First, run screen -list to get the id of the current sessions (we use the id to kill the screen session)

    daz@scampi:~$ screen -list
There are screens on:
11493.irssi     (04/01/10 16:25:44)     (Detached)
30784.newapps   (01/01/10 19:42:38)     (Detached)

    As you can see in this example, I have two sessions, a session called “irssi” with id 11493, and a session called “newapps”, with an id of 30784.

    So, to kill the “newapps” session, I’d run:

    daz@scampi:~$ screen -X -S 30784 kill
daz@scampi:~$

    .. and the session will now be gone.  You can verify that by running screen -list again.

    Killing by session name

    If your screen session name is unique enough (for example, if you have one called “newapps” and another called “irssi” as per my example) you can kill by name:

    daz@scampi:~$ screen -X -S newapps kill
daz@scampi:~$

    The reason I say unique enough –  if you have a session called “newapps” and one called “newapps1″, you will need to use the ID to end “newapps” before “newapps1″ – you’ll simply be asked to specify the session again otherwise.

     

  • Finding out when (and where from) a user last logged into a Linux/BSD machine

    00:21 on January 2, 2010 | 0 Comments Tweet This! | Digg This!
    Tags: bsd, ,

    There may be times when you want to find out when and where from a user last logged into a Linux or BSD machine.

    Of course, you could trawl through auth logs, but there is a quicker way by using “lastlog“.

    lastlog is a command which shows you the last login time and also from where (if it was a remote session, it’ll show you the IP/Hostname) a user logged in.

    If you log into the machine and at a terminal run, you’ll get the information:

    droptips@server:~$ lastlog
Username         Port     From             Latest
root                                       **Never logged in**

    (I’ve removed all of my information for security reasons)

    There is a man page available for “lastlog” accessible via:

    droptips@server:~$  man lastlog

    You can also read the Ubuntu 9.10 man page for lastlog here: http://manpages.ubuntu.com/manpages/karmic/man8/lastlog.8.html
    The Wikipedia page is here:  http://en.wikipedia.org/wiki/Lastlog
     

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