Practical Exercises To be completed by 4/10/2008

Login scripts; checking the run sequence.

In a user home directory (non-root), there should be scripts .bash_profile and .bashrc. In /root, there would be .profile instead of .bash_profile.
Create a new user account, for example jerry:

useradd -m -s /bin/bash jerry

In file .bash_profile, put entry

echo BASH_PROFILE

In file .bashrc, put entry

echo BASHRC

Create files .bash_login and .profile with the only entries echo BASH_LOGIN and echo PROFILE, accordingly.
Logout and login as user jerry and notice BASH_PROFILE in the login prompt. Start a new shell,

/bin/bash

notice BASHRC in the new shell prompt.
Remove file .bash_profile, logout and login as user jerry again. Notice BASH_LOGIN in the new login prompt.
Remove file .bash_login, logout and login as user jerry again. Notice PROFILE in the login prompt.

Switching between run levels.

Modify /etc/inittab to boot into default Run Level 5; reboot the system using /sbin/init 6 command. When the system boots up, verify the current run level with command

/sbin/runlevel

Change sequentially to Run Levels 3, 2, and 1 using command

/sbin/init N

where N is the next Run Level. Run /sbin/runlevel command in every Run Level.

Modify file /etc/inittab to disable authentication in the single user mode:

#~:S:wait:/sbin/sulogin
~:S:wait:/bin/bash

Make init to re-read /etc/inittab by executing command

/sbin/telinit q

Enter Run Level 1 to verify if you don't get prompt for password.

Adding and removing system services from the startup

Remove portmap, nfs-common, nfs-kernel-server, and exim4 from the startup:

update-rc.d -f portmap remove 
update-rc.d -f nfs-common remove 
update-rc.d -f nfs-kernel-server remove 
update-rc.d -f exim4 remove

Add portmap, nfs-common and nfs-kernel-server to the startup to start in Level 3 and stop in Levels 0 1 2 6:

update-rc.d portmap start 20  3 . stop 20  0 1 2 6 .
update-rc.d nfs-common start 21  3 . stop 21  0 1 2 6 .
update-rc.d nfs-kernel-server start 21  3 . stop 21  0 1 2 6 .

Add exim4 to the startup to start in Level 2 and stop in Levels 0 1 3 6:

update-rc.d exim4 start 20 2 . stop 20 0 1 3 6 .

Enter Run Level 3 and check which of the above services are running.

ps -ef | grep exim
ps -ef | grep portmap
ps -ef | grep rpc

Enter Run Level 2 and check which of the above services are running.

Creating startup scripts.

Copy the script from the lecture, sample.sh, in /etc/init.d directory; make it executable; try to run it:

   
   /etc/init.d/sample.sh
   /etc/init.d/sample.sh start
   /etc/init.d/sample.sh stop

Create symbolic links of the script to various /etc/rcN.d directories:

   ln -s /etc/init.d/sample.sh /etc/rc1.d/K99sample  
   ln -s /etc/init.d/sample.sh /etc/rc2.d/S99sample  
   ln -s /etc/init.d/sample.sh /etc/rc3.d/K99sample

Init to Run Levels 1, 2, and 3 and notice if the init runs S99sample and K99sample scripts: check the updated content of file /var/log/sample.log Remove the links. Set the script to "stop" at run level 1, 3, and 5 and "start" at Run Levels 2 and 4:

update-rc.d sample.sh start 20  2 4 . stop 20  1 3 5 .

Check what kind of links with sample.sh have been created in /etc/rc1.d /etc/rc2.d, /etc/rc3.d, /etc/rc4.d and /etc/rc5.d
Remove the log file

rm /var/log/sample.log

Enter Run Levels 1, 2, 3, 4, and 5. Check the content of file /var/log/sample.log.

Scheduled jobs through at and cron.
Create a script, mem.sh, to check memory status:

#!/bin/sh
# Checks memory status through cron

of=/home/$USER/mem.out
dt=`date`

echo "Memory status (in MB) on $dt:" >> $of 
free -m >> $of
echo "------------------" >> $of

Make it executable and run through at:

at -f mem.sh now + 1 minute

Run atq to make sure the job is scheduled. In a minute, check content of a new file, mem.out; run atq again.

Remove file mem.out. Modify the script specifying the full path to your home directory in "of", i.e. "of=/home/your_username/mem.out". Add the following entry in /etc/crontab before the line "# run-parts":

*/2 * * * *  root  /home/your_username/mem.sh

Check if the content of mem.out is updated every 2 minutes.

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