10 Linux commands you’ve Never Used

Nice blog entry detailing: pgrep, pstree, bc, split, nl, mkfifo, ldd, col, lsof, xmlwf

I also want to go on record that I HAVE used 5 of them.

cron Format (crontab)

* * * * * command to be executed
- - - - -
| | | | |
| | | | ----- day of week (0 - 6) (Sunday=0)
| | | ------- month (1 - 12)
| | --------- day of month (1 - 31)
| ----------- hour (0 - 23)
------------- min (0 - 59)

Show Solaris Configuration

Try these commands to get hardware info:

prtconf

vmstat

dmesg

Using Top Efficiently

Here is a link disussuing using TOP to create performance snapshots and other tips.

PERL for search and replace

You can use PERL as a stream editor to replace strings in one or more files in a directory like this:

perl -pi.orig -e ‘s/bgcolor=#ffffff/bgcolor=#000000/i’ *.html

The above replaces the color white with black in all html files in this directory and saves the original files with .orig extension.

Keep local environment when logging to remote servers

Use the script movein.sh from O’Reilley.

#!/bin/sh

if [ -z "$1" ]; then
echo "Usage: `basename $0` hostname"
exit
fi

cd ~/.skel
tar zhcf - . | ssh $1 "tar zpvxf -"

Read link for more info...

Generate SSL Certificate

Need OpenSSL for this -

openssl genrsa 512/1024 http://www.mysite.com.key
openssl req -new -key http://www.mysite.com.key >  http://www.mysite.com.csr

Enter country, state, locality, org name, org unit, comon name, and email when asked. Note: Common Name is http://www.mysite.com.

openssl -req -x509 -key http://www.mysite.com.key -in http://www.mysite.com.csr http://www.mysite.com.crt

ssh Tips

X over ssh: ssh -X hostname

Forward port over ssh:
ssh -f -N -L110:mailhost:110 -l user mailhost

nmap Get remote system o/s and more

To find out what type of machine a host is, type:

nmap -O host

Compare services on your server or subnet, run this at 2 different times and then diff the files -

nmap -sX 10.14.34.0/24 | egrep -v '^(Nmap|Starting)' > nmap.out.date

Use watch for repeated commands

Instead of constantly typing ‘ps -ef|grep yada’ over and over, use watch to highlight differences and tell you when the command finishes.

watch 'ps -ef|grep tar'

Removing a user’s access (but not his files)

#Lock acct
passwd -l user

#Move directory to avoid .ssh, .rhosts, etc
mv /home/user /home/user.removed

#Check for running jobs
ps awux | grep -i ^user
skill -KILL user

#Check for cron jobs
crontab -u user -e

#remove user from sudo users file if needed

pgrep and pkill

If you want to find out the process IDs for all process names containing ‘httpd’ -

pgrep httpd
321
324
455

If you want to kill all httpd processes -

pkill httpd

/proc commands

Find running kernel version:

cat /proc/version

How much RAM is installed:

ls -l /proc/kcore

Take file size and divide by 1024*1024

sudo User Format with Alias

sudo users file format is as follows:

user machine=(effective user) commands

Aliases in any part are allowed and reference via all CAPS; UNIX group names are started with %.

User_Alias ADMINS=rob,jim,joep
root ALL=(ALL) ALL
joep elvis=(www) /bin/safe_mysqld,/usr/bin/top
ADMINS ALL=(bind) ALL
%staff ALL=(guest) ALL

Can’t remove files as root

In the ext2/ext3 filesystems sometimes you can’t remove a file even if you are root! This means the immutable flag is set. You can check it with the lsattr command. You can change it (or set it) with ‘chmod -i file‘.