Many Linux distributions are preconfigured to automatically and periodically rotate syslog log files by means of cron jobs that call logrotate or a similar log rotation script. However, if you want to clear a log file manually, you can simply use the greater than sign followed by the log file name. For example, to manually clear the file kern.log, you can run this command:
me@mycomputer:> /var/log/kern.log
The beauty of this is that the cleared out file still retains its original permissions and ownership.
I often use Linux’s netstat command to do things like figuring out which ports are listening on a computer and what are the active connections on a computer. It’s very handy for troubleshooting networking problems.
Today I wanted to figure out what sites a certain user on my network was connecting to and how much traffic the user was using. I connected to the router with SSH and ran netstat with no options. I was surprised to see only my SSH connection. Then I remembered that the user in question gets onto the internet with a masqueraded address. Well, duh! …Continue reading » Displaying Masqueraded Connections
Anyone who has used Linux traceroute and Windows tracert knows that the two programs have very different command line options. But did you know that there is a fundamental difference in the way that these two programs work? …Continue reading » Linux traceroute vs Windows tracert
To sort files by modification time when using ls, use the -t option. For example, to sort in descending order:
[me@mycomputer usr]$ ls -lt
total 224
drwxr-xr-x 88 root root 65536 Sep 1 17:39 lib
drwxr-xr-x 14 root root 4096 Sep 1 16:00 local
drwxr-xr-x 2 root root 12288 Jul 26 04:04 sbin
drwxr-xr-x 174 root root 4096 Jul 25 19:01 share
drwxr-xr-x 2 root root 40960 Jan 25 2006 bin
drwxr-xr-x 7 root root 4096 Jan 16 2006 libexec
drwxr-xr-x 3 root root 4096 Oct 16 2005 java
drwxr-xr-x 61 root root 12288 Mar 13 2005 include
drwxr-xr-x 4 root root 4096 Mar 13 2005 src
lrwxrwxrwx 1 root root 10 Mar 13 2005 tmp -> ../var/tmp
drwxr-xr-x 6 root root 4096 Feb 27 2005 kerberos
drwxr-xr-x 2 root root 4096 Feb 22 2005 etc
drwxr-xr-x 2 root root 4096 Feb 22 2005 games
drwxr-xr-x 7 root root 4096 Feb 21 2005 X11R6
To sort in descending order, add the -r option:
[me@mycomputer usr]$ ls -ltr
total 224
drwxr-xr-x 7 root root 4096 Feb 21 2005 X11R6
drwxr-xr-x 2 root root 4096 Feb 22 2005 games
drwxr-xr-x 2 root root 4096 Feb 22 2005 etc
drwxr-xr-x 6 root root 4096 Feb 27 2005 kerberos
lrwxrwxrwx 1 root root 10 Mar 13 2005 tmp -> ../var/tmp
drwxr-xr-x 4 root root 4096 Mar 13 2005 src
drwxr-xr-x 61 root root 12288 Mar 13 2005 include
drwxr-xr-x 3 root root 4096 Oct 16 2005 java
drwxr-xr-x 7 root root 4096 Jan 16 2006 libexec
drwxr-xr-x 2 root root 40960 Jan 25 2006 bin
drwxr-xr-x 174 root root 4096 Jul 25 19:01 share
drwxr-xr-x 2 root root 12288 Jul 26 04:04 sbin
drwxr-xr-x 14 root root 4096 Sep 1 16:00 local
drwxr-xr-x 88 root root 65536 Sep 1 17:39 lib
