Tag Archives: GNU

GNU and UNIX Commands: Using a while Loop to Populate Configuration File

I recently had a need to generate a lot of Nagios host definitions. The hosts all had a similar naming convention:

foo-nnnnprjenv

Here, nnnn was a zero-padded number from 0 to 9999. In this particular environment, there were 41 hosts. A simple multiline echo command inside a while loop fed by seq produces the appropriate host stanzas we can add to our Nagios configuration. We also look up the servers IP addresses via the host command and insert those too:

$ seq -w 1 41 | while read num; do
   echo "define host {
        use             generic-host
        host_name       foo-00${num}prjenv
        alias           foo-00${num}prjenv
        address         $( host foo-00${num}prjenv | awk '{print $NF}' )
        register        1
}
"
done

$ seq -w 1 41 | while read num; do

echo "define host {

use generic-host

host_name foo-00${num}prjenv

alias foo-00${num}prjenv

address $( host foo-00${num}prjenv | awk '{print $NF}' )

}

done

The -w option to seq causes it to output a leading-zero padded number. Redirect the output of this loop to a file, and you’ll have your Nagios host configuration. This is another reasons why having a naming convention for a large number of servers is important - it will aid you in automation and administration down the track.

GNU and UNIX Commands: Sending HTML-formatted email from the Command Line

Some brief notes I made on sending HTML mail (with an optional attachment) from the command line.

$ cat ./mailheader
To: you@there.com
From: me@here.com
MIME-Version: 1.0
Content-Type: text/html; charset=us-ascii
Subject: Hello
$ cat ./mailbody
<center><h1>Hello</h1></center>
$ cat ./mailheader ./mailbody | /usr/lib/sendmail -t
# send an attachment too?
$ ( cat ./mailheader ./mailbody && uuencode attachment.txt attachment.txt ) | /usr/lib/sendmail -t

$ cat ./mailheader

To: you@there.com

From: me@here.com

MIME-Version: 1.0

Content-Type: text/html; charset=us-ascii

Subject: Hello

$ cat ./mailbody

<center><h1>Hello</h1></center>

$ cat ./mailheader ./mailbody | /usr/lib/sendmail -t

# send an attachment too?

$ ( cat ./mailheader ./mailbody && uuencode attachment.txt attachment.txt ) | /usr/lib/sendmail -t

GNU and UNIX Commands: Find Out Which Ports a Program is Listening on

This is easiest done with lsof. On Solaris you can use pfiles, and you may also find netstat -anlp on Linux useful.

First, find the PID of the process you’re interested in

# ps -ef | grep '[v]m'
root     32702     1  0 Mar08 ?        00:00:00 /usr/bin/vmpsd

1 2	# ps -ef \| grep '[v]m' root 32702 1 0 Mar08 ? 00:00:00 /usr/bin/vmpsd

Then, run lsof against the PID

# lsof -p 32702
COMMAND   PID USER   FD   TYPE             DEVICE    SIZE    NODE NAME
vmpsd   32702 root  cwd    DIR                9,1    4096       2 /
vmpsd   32702 root  rtd    DIR                9,1    4096       2 /
vmpsd   32702 root  txt    REG                9,1   23708  881217 /usr/bin/vmpsd
vmpsd   32702 root  mem    REG                0,0               0 [heap] (stat: No such file or directory)
vmpsd   32702 root  mem    REG                9,1 1184892 1024170 /lib32/libc-2.4.so
vmpsd   32702 root  mem    REG                9,1  124785 1024169 /lib32/ld-2.4.so
vmpsd   32702 root    0u   CHR              136,0               2 /dev/pts/0 (deleted)
vmpsd   32702 root    1u   CHR              136,0               2 /dev/pts/0 (deleted)
vmpsd   32702 root    2u   CHR              136,0               2 /dev/pts/0 (deleted)
vmpsd   32702 root    3u  IPv4            4214826             UDP *:1589
vmpsd   32702 root    4u  unix 0xffff81007d816300         4214827 socket

# lsof -p 32702

COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME

vmpsd 32702 root cwd DIR 9,1 4096 2 /

vmpsd 32702 root rtd DIR 9,1 4096 2 /

vmpsd 32702 root txt REG 9,1 23708 881217 /usr/bin/vmpsd

vmpsd 32702 root mem REG 0,0 0 [heap] (stat: No such file or directory)

vmpsd 32702 root mem REG 9,1 1184892 1024170 /lib32/libc-2.4.so

vmpsd 32702 root mem REG 9,1 124785 1024169 /lib32/ld-2.4.so

vmpsd 32702 root 0u CHR 136,0 2 /dev/pts/0 (deleted)

vmpsd 32702 root 1u CHR 136,0 2 /dev/pts/0 (deleted)

vmpsd 32702 root 2u CHR 136,0 2 /dev/pts/0 (deleted)

vmpsd 32702 root 3u IPv4 4214826 UDP *:1589

vmpsd 32702 root 4u unix 0xffff81007d816300 4214827 socket

Port 1589/UDP, that’s the information we wanted.

GNU and UNIX Commands: grep with AND instead of OR

We all know how easy it is to grep for something OR something_else:

egrep 'something|something_else' filename

1	egrep 'something\|something_else' filename

However, there’s no elegant way to grep for something AND something_else:

# This works, but is ugly
grep 'something' filename | grep 'something_else'
# This works, but searchterms must appear in the same order within the file
grep 'something.*something_else' filename

# This works, but is ugly

grep 'something' filename | grep 'something_else'

# This works, but searchterms must appear in the same order within the file

grep 'something.*something_else' filename

Easiest way around this (and most elegant) is with awk:

awk '$0 ~ /something/ && $0 ~ /something_else/ 1;' filename

1	awk '$0 ~ /something/ && $0 ~ /something_else/ 1;' filename

GNU and UNIX Commands: GNU date and the -d option

If your system has GNU date installed, you can perform some very cool and quick date arithmetic with the -d option. For example:

$ # get yesterdays date and format the output
$ date -d "yesterday" +"%d %b %Y"
10 Jan 2005
$ # get the date in two mondays time
$ date -d "next 2 monday"
Mon Jan 17 00:00:00 GMTST 2005
$ # 3 weeks ago
$ date -d "3 weeks ago"
Wed Dec 20 14:06:44 GMTST 2004

$ # get yesterdays date and format the output

$ date -d "yesterday" +"%d %b %Y"

10 Jan 2005

$ # get the date in two mondays time

$ date -d "next 2 monday"

Mon Jan 17 00:00:00 GMTST 2005

$ # 3 weeks ago

$ date -d "3 weeks ago"

Wed Dec 20 14:06:44 GMTST 2004

You get the idea. Read the man and info pages for date for further information!

How to Format seq Output

seq comes with the -f option, allowing us to specify a printf(3) format string.

For example, to zero pad seq output (five zeros):

$ seq -f %05g 1 10
00001
00002
00003
00004
00005
00006
00007
00008
00009
00010

$ seq -f %05g 1 10

00001

00002

00003

00004

00005

00006

00007

00008

00009

00010

See: seq(1) printf(3)

Toki Winter

Advanced UNIX for the experienced system administrator