Automatically logout inactive SSH sessions

Typically in an Enterprise setup, we would see Users login from various terminals via SSH but never bother to disconnect the established session. This might cause a slight overload on the Network, since these Established sessions have to maintain their connections by sending Alive packets. So I guess it would be appropriate if we make these Users automatically Logout after a certain period of Inactivity (say 1 hour).

Solution 1:

Create a file called "autologout.sh" under /etc/profile.d with execute permission.

# touch /etc/profile.d/autologout.sh

# chmod 711 /etc/profile.d/autologout.sh

Add the following entries to it (Assuming we have to automatically Logout the users after 1 hour, which is 3600 seconds).

TMOUT=3600

readonly TMOUT

export TMOUT

Solution 2:

Enable the following directives in SSH config file (/etc/ssh/sshd_config) and reload the 'sshd' service.

ClientAliveInterval 3600

ClientAliveCountMax 0

# service sshd reload  (or)  # service sshd restart

Few useful Bash Shell shortcuts

Ctrl + l       # Clear the screen
Ctrl + u      # Delete backward from the cursor position
Ctrl + k      # Delete till End of Line
Ctrl + r      # Search the History from backwards
Ctrl + e     # Move the cursor to end of line


Alt + Back-space      # Delete backwards word by word
Alt + t                      # Shuffle words
Alt + b                     # Move backwards
Alt + f                      # Move forwards


Press 2 times Tab key       # Lists all available commands on the server
$ with 2 times Tab key       # Display all system variables
Some string followed by 2 times Tab key     # All available commands starting with that string  


Refer: http://wiki.bash-hackers.org/syntax/shellvars

Analyzing past System performance of a Linux server

Assumption: 

Today's date is 13th Aug, 2011.  You are asked to check the System performance of a Linux server on 7th Aug,2011 between 3 AM to 5 AM.

Solution: 

Run the 'sar' command on the respective 'sa' (System Activity) file created for the date "7th Aug,2011" with specifying the Starting and End time.

Illustration:

Go to /var/log/sa

[root@hostxyz sa]# ls -ltr sa??

-rw-r--r-- 1 root root 481776 Aug 5 23:50 sa05
-rw-r--r-- 1 root root 481776 Aug 6 23:50 sa06
-rw-r--r-- 1 root root 481776 Aug 7 23:50 sa07       # File that belongs to 7th Aug,2011
-rw-r--r-- 1 root root 481776 Aug 8 23:50 sa08
-rw-r--r-- 1 root root 481776 Aug 9 23:50 sa09
-rw-r--r-- 1 root root 481776 Aug 10 23:50 sa10
-rw-r--r-- 1 root root 481776 Aug 11 23:50 sa11
-rw-r--r-- 1 root root 481776 Aug 12 23:50 sa12
-rw-r--r-- 1 root root 287824 Aug 13 14:10 sa13

[root@hostxyz sa]#
[root@hostxyz sa]# sar -u -f /var/log/sa/sa07 -s 03:00:01 -e 05:00:01   # To check CPU utilization
Linux 2.6.18-92.el5 (hostxyz) 08/07/2011

03:00:01 AM CPU %user %nice %system %iowait %steal %idle
03:10:01 AM all 24.57 0.00 5.16 6.04 0.00 64.23
03:20:01 AM all 24.57 0.10 5.06 6.28 0.00 63.98
03:30:01 AM all 24.33 0.00 4.88 5.64 0.00 65.14
03:40:01 AM all 15.75 0.00 3.93 10.52 0.00 69.80
03:50:01 AM all 12.70 0.00 3.09 19.04 0.00 65.17
04:00:01 AM all 16.80 0.00 3.90 9.40 0.00 69.90
04:10:01 AM all 9.18 0.02 2.26 14.43 0.00 74.11
04:20:01 AM all 8.84 0.10 2.20 9.65 0.00 79.22
04:30:01 AM all 11.42 0.00 3.24 10.50 0.00 74.84
04:40:01 AM all 11.84 0.00 2.43 20.64 0.00 65.09
04:50:01 AM all 17.80 0.00 3.78 17.00 0.00 61.42
05:00:01 AM all 6.46 0.00 1.53 21.80 0.00 70.22
Average: all 15.35 0.02 3.46 12.58 0.00 68.59

[root@hostxyz sa]#

[root@hostxyz sa]#  sar -r -f /var/log/sa/sa07 -s 03:00:01 -e 05:00:01    # To check Memory status

[Output no shown]
.

[root@hostxyz sa]#  sar -q -f /var/log/sa/sa07 -s 03:00:01 -e 05:00:01    # To check Load average

[Output not shown]

.

[root@hostxyz sa]#  sar -b -f /var/log/sa/sa07 -s 03:00:01 -e 05:00:01     # To check I/O status

[Output not shown]

.

[root@hostxyz sa]#  sar -n DEV -f /var/log/sa/sa07 -s 03:00:01 -e 05:00:01    # To check Network status

[Output not shown]

.

[root@hostxyz sa]# 

Notes: In Linux, System activity report is collected for every 10 minutes by a cron job "sysstat" located under /etc/cron.d and at end of the day, a summary report is generated and saved in /var/log/sa/saXX file, which we can use for later analysis. 

[root@hostxyz cron.d]# cat sysstat

# run system activity accounting tool every 10 minutes

*/10 * * * * root /usr/lib64/sa/sa1 1 1

# generate a daily summary of process accounting at 23:53
53 23 * * * root /usr/lib64/sa/sa2 -A

root@hostxyz cron.d]#

Sending mail using 'mutt' from shell

In my opinion, 'mutt' is the best text-based Email client for sending mails with Attachment from Linux shell. The best part with it is, it supports wide variety of MIME ("Multipurpose Internet Mail Extensions") types, which ensures the integrity of various types of attachments such as Binary, jpeg, mp3 files.

Below shown are few command sets for sending mails using Mutt with following specifications.

To address: rdashokraj@yahoo.com

Subject: Test mail

Attachment filename:  song.mp3

Message body:  "This mail has a mp3 attachment"

With attachment:

# echo "This mail has a mp3 attachment" | mutt -s "Test mail" -a song.mp3 rdashokraj@yahoo.com

# mutt -s "Test mail" -a study.dat rdashok@outlook.com < messagefile 

Note: "messagefile" is the filename that contains the message body "This mail has a mp3 attachment"

Without attachment:

# echo "Mail without attachment" | mutt -s "Test mail" rdashok@outlook.com

Without Message body:

# mutt -s "Test mail" -a study.txt rdashok@outlook.com < /dev/null