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

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

Today I had to add an existing user to an existing group in Linux. It’s been so long since the last time I did it that I had actually forgotten how to do it. Well, good ol’ man pages to the rescue. Here’s how to do it:

adduser user group

If you want to verify that it worked, use grep:

grep group /etc/group

In grep’s output, you should see the user’s name. For example:

group:!:50:tom,dick,harry,user

Enjoy!