ISR Computing -

Tricky RHCE questions

• How to find out which init level you are in?

[root@rhel5 ~]# ps -ef | more
UID        PID  PPID  C STIME TTY          TIME CMD
root         1     0  0 22:42 ?        00:00:00 init [5]  

Scheduler is process 0; init is process 1;

• How to get inode information?

[root@rhel5 ~]# ls -i anaconda-ks.cfg 
370783 anaconda-ks.cfg
[root@rhel5 ~]# 

• How to debug shell script?

To turn debug on:

set -x

To turn debug off:

set +x

• Another way is to create function inside shell script:

#!/bin/bash
_DEBUG="on"
function DEBUG()
{
 [ "$_DEBUG" == "on" ] && $@ || :
}
DEBUG echo 'Reading files'
for i in *
do
 grep 'something' $i > /dev/null
 [ $? -eq 0 ] && echo "Found in $i file" || :
done
DEBUG set -x
a=2
b=3
c=$(( $a + $b ))
DEBUG set +x
echo "$a + $b = $c"

• How to get list of local users

[root@rhel5 ~]# cat /etc/passwd |grep "/home" |cut -d: -f1
vernon
olivia
garry

• How to delete files in /tmp directory, that match pattern "workspace.*" and are 7 days old?

find /tmp -name workspace.* -mtime +7 -maxdepth 1 | more
find /tmp -name workspace.* -mtime +7 -maxdepth 1 -exec rm -f {} \;

• How to Process Shell Output with Perl?

zcat oui.txt | perl -ne 'if ($_ =~ m/(\w{2})-(\w{2})-(\w{2})\s+\(hex\)\s+(.*)/) { print lc($1).lc($2).".".lc($3).",$4\n"; }'