July 25, 2005

CLI Magic: Information, please

Author: Joe Barr

There are lots of ways the CLI can help you. Often, you don't need to do something so much as you need to know something. This week we'll take a quick look at several commands -- whereis, whatis, df, kernelversion, ifconfig, route, and last -- that can quickly answer questions about your system or configuration. Wipe that GUI mess out of your eyes and meet me at the CLI. Where is that darn command?

You know the command is on your system, because you've used it before. But now you can't remember where it lives. Is it in /sbin? Or /usr/bin? Somewhere else? The whereis command is designed to answer that very question. In fact, whereis will tell you not only where to find the executable command, but the source code -- if it's present -- and man pages as well. All you need to do is ask, by providing the name of the command you're looking for:

warthawg@linux:~> whereis whatis
whatis: /usr/bin/whatis /usr/share/man/man1/whatis.1.gz

What is that command for?

Maybe you've heard people mention a command, but aren't sure what it does. All you have to is ask. Here's a metaphysical example to consider:

warthawg@linux:~> whatis time
time (1)             - time a simple command or give resource usage
time (2)             - get time in seconds
time (n)             - Time the execution of a script
time (1p)            - time a simple command
time (3p)            - get time

How much disk space do I have left?

An excellent question to ask from time to time, and especially before a critical drive fills up completely. To get the answer, type df on the command line. This handy little utility shows you how much space you've used and how much is left in every mounted file system. Like this:

warthawg@linux:~> df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hdc1             19550436   3493984  16056452  18%
tmpfs                   517572         0    517572   0% /dev/shm
/dev/hda2              7847500     32840   7814660   1% /downloads
/dev/hdd1            115380192  39944740  69574416  37% /home

I'm running the 2.4 kernel, what about you?

If you hang around Linux people very long, whether it's a LUG meeting or online chat, someone is going to ask what version of the kernel you're running. There's a command to tell, just in case you forget:

warthawg@linux:~> /sbin/kernelversion
2.6

What's my IP address?

Sometimes you just have to know your IP address. Entering ifconfig without any arguments is one way to find out, and learn a lot more as well:

warthawg@linux:~> /sbin/ifconfig
eth0      Link encap:Ethernet  HWaddr 00:50:8D:4E:9D:D0
          inet addr:192.168.0.101  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::250:8dff:fe4e:9dd0/64 Scope:Link
          UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:74969 errors:0 dropped:0 overruns:0 frame:0
          TX packets:76379 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:54194289 (51.6 Mb)  TX bytes:12136154 (11.5 Mb)
          Interrupt:11 Base address:0xe800

How do I get to the Internet from here?

OK, you found out what your IP address is -- even if it is private, like the one above -- but how do you talk to the Internet? The route command can give you the answer. No arguments required:

warthawg@linux:~> /sbin/route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.0.0     *               255.255.255.0   U     0      0        0 eth0
link-local      *               255.255.0.0     U     0      0        0 eth0
loopback        *               255.0.0.0       U     0      0        0 lo
default         192.168.0.1     0.0.0.0         UG    0      0        0 eth0

As you can see, my default gateway has an IP address of 192.168.0.1. In my case, that's my router, which talks to the LAN on one side and to the cable modem/Internet on the other.

At last

Last we have last. Enter it without any arguments and it will show you the last system signons to your system, going as far back as the log files allow it to go. The output looks like this:

warthawg pts/0 :0.0             Mon Jul 18 16:43   still logged in
warthawg pts/0 :0.0             Mon Jul 18 16:42 - 16:42  (00:00)
warthawg pts/0 :0.0             Mon Jul 18 16:40 - 16:40  (00:00)
warthawg pts/3 :0.0             Mon Jul 18 15:35 - 15:39  (00:04)
warthawg pts/2 :0.0             Mon Jul 18 14:47   still logged in
warthawg pts/0 :0.0             Mon Jul 18 14:36 - 16:34  (01:58)
warthawg pts/0 :0.0             Mon Jul 18 14:23 - 14:36  (00:13)
warthawg pts/0 :0.0             Mon Jul 18 14:20 - 14:23  (00:02)
warthawg pts/2 :0.0             Mon Jul 18 14:07 - 14:18  (00:11)
warthawg pts/2 :0.0             Mon Jul 18 13:44 - 13:45  (00:01)
warthawg pts/0 :0.0             Mon Jul 18 11:52 - 14:07  (02:15)

There you have it. A tease on seven different commands you can use to get information about your system. Many of them allow arguments that you can use to tune and modify the output. If any of these have caught your fancy, do the man thing.

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