Linux

Looking for a log to show you failed login attempts to your Linux machine? Look in:
/var/log/btmp
You can access it by running:
/usr/bin/lastb
It’s similiar to the wtmp log of user login/logouts and the utmp log showing who is currently logged in.

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I install RHEL on all my production machines and CentOS on all my test/development boxes. Installing the GUI is helpful for configuration, but you sure don’t want to run them that way all the time. So after everything is installed, configured and tested, I make the following change:
nano /etc/inittab
Change
id:5:initdefault:
To
id:3:initdefault:
Save the file and reboot the machine. [...]

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nano /etc/sysconfig/network-scripts/ifcfg-eth0
Should look something like this

DEVICE=eth0
BOOTPROTO=static
BROADCAST=172.16.0.255
HWADDR=00:00:00:00:00:00
IPADDR=172.16.0.2
NETMASK=255.255.255.0
NETWORK=172.16.0.0
ONBOOT=yes
Duplicate that and open the new file
cp /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-eth0:0
nano /etc/sysconfig/network-scripts/ifcfg-eth0:0
Change device name, set new IP, remove reference to hardware

DEVICE=eth0:0
BOOTPROTO=static
BROADCAST=172.16.0.255
IPADDR=172.16.0.3
NETMASK=255.255.255.0
NETWORK=172.16.0.0
ONBOOT=yes

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I use wget all the time on my Linux machines, but was surprised to find it missing on my MacBook Pro. Since Mac OS is based on BSD, it uses cURL instead. Here’s a good way to scrape files from a remote server.
curl -O http://www.gutenberg.org/files/21171/mp3/21171-[01-24].mp3
Man page is available at: http://curl.haxx.se/docs/manpage.html

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After a few months of continuous use, I’ve found Ensim to start using too much swap space and getting sluggish. A quick restart via command line, always fixes both:
/etc/init.d/epld restart

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It’s easy to pause a shell script during execution. Just add:
sleep 10
(where 10 is the number of seconds you want the script to pause.)
Some code for testing would be…
#!/bin/sh
before=”$(date +%s)”
echo $before
sleep 3
after=”$(date +%s)”
echo $after
elapsed_seconds=”$(expr $after - $before)”
echo Elapsed time for code block: $elapsed_seconds

Have other ideas? Please comment.

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find /somedir -type f -size +50000k -mtime +1095 -exec ls -lh {} \; | awk ‘{ print  $6 “/” $8 ” ” $9 $10  $11 “: ” $5 }’

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#!/bin/sh
before=”$(date +%s)”
echo $before
sleep 5
Ymd=”$(date ‘+%Y%m%d’)”
echo $Ymd
after=”$(date +%s)”
echo $after
elapsed_seconds=”$(expr $after - $before)”
echo Elapsed time for code block: $elapsed_seconds

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I occasionally get this error when trying to run a heyu command from CLI. This should fix your problem:
(As root)
chmod 777 /dev/ttyS0

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