Script to generate Complex password

Description:
This script can be used to generate complex password with predefined password length.

Script:
#!/bin/bash
#Filename : randompass.sh

#Sets the length of the password the script will generate
MAXSIZE=8
# Holds valid password characters. I choose alpha-numeric + the shift-number keyboard keys
array1=(
w e r t y u p a s d f h j k z x c v b m Q W E R T Y U P A D
F H J K L Z X C V B N M 2 3 4 7 8 ! @ $ % \# \& \* \= \- \+ \?
)

# Used in conjunction with modulus to keep random numbers in range of the array size
MODNUM=${#array1[*]}

# Keeps track of the number characters in the password we have generated
pwd_len=0

while [ $pwd_len -lt $MAXSIZE ]
do
  index=$(($RANDOM%$MODNUM))
  password="${password}${array1[$index]}"
  ((pwd_len++))
done
echo $password


Sample Execution: 
[root@sysllm01 create_password]# ./random_pass.sh
#V?Z27NN
[root@sysllm01 create_password]# ./random_pass.sh
D34EXL*3
[root@sysllm01 create_password]#

Find syntax to list huge-sized files and calculate total size

Situation

The disk space in one of the file-system (say /data1) is more 90% and you are asked to list out all the files which are more than 100 MB size and find the sum of total space occupied by listed files in Megabytes.

Solution

To list all the files in /data1, which are more than 100 MB size.

# find /data1 -size +102400k -exec du -sh {} \;

To find the sum of total space occupied by listed files.

In Megabytes:

# find /data1 -size +102400k -ls | awk '{sum += $7} END {printf "Total size: %8.4f MB\n", sum/1024/1024}'\;

In Gigabytes:

# find /data1 -size +102400k -ls | awk '{sum += $7} END {printf "Total size: %6.2f GB\n", sum/1024/1024/1024}'\;

Command-line to check the details of Perl modules installed on Linux

To find the path of Perl modules installed:  
# perl -e 'print join "\n", @INC'

To find the path of each individual Perl modules:
# find `perl -e 'print "@INC"'` -name '*.pm' -print

To check if a given Perl module is installed on the system:
Let say you want to check if the Perl module "File::Compare" is installed or not. The syntax would be as follows:
# perl -e 'use File::Compare; print "Installed\n"'
Installed
#

How to reset the permissions of installed RPM packages ?

Situation:  

One of our Developer has changed the permission of all the files under /etc to 777 by inadvertently executing the chmod command with 777 permission. Due to this, the system went into non-usable state.

Resolution: 

The Linux 'rpm' command  comes with an interesting switch known as '--setperms' using which we can restore the file-permissions of either one or more packages. 

Syntax:  

# rpm --setperms [package name]

To reset one specific RPM package:  

# for pkg in $(rpm -qa | grep -w pkgname); do rpm --setperms $pkg; done
Example:  
To reset the 'zip' package.
# rpm -qa | grep zip                           <-- Check to see if the package exists
# for pkg in $(rpm -qa | grep -w zip); do rpm --setperms $pkg; done

To reset the entire packages installed ( applicable in the situation I mentioned above):

# for allpkg in $(rpm -qa); do rpm --setperms $allpkg; done

Note:  To restore the Group permission, we need to use the switch "--setugids".

Linux system info script - latest version

Whenever I work on Performance issue of a Linux server or when I do any Server Audit, I used to wonder how great it would be if I have a script that will give me all the vital information about the system including the Health status and Security settings. I put my thought into action and this Perl script is a result of it.

Upon execution with the syntax "perl sysinfo.pl", it will display all the vital System parameter details, Health Status and the Security Information on ONE screen.

Supported Platform :  Any Physical or VMware Server running on Linux OS with Perl installed.

Packages required : The Linux machine should contain 'sysstat' and 'dmidecode-2.xx' package,

URL to download the script: https://tinyurl.com/yb97snab
Once you download, please run the following command to convert the script into Unix format: # dos2unix sysinfo.pl

SAMPLE OUTPUT

Note: I shall keep adding new features to this script. Hence please use the given download link to get the latest version.

PS: The Logics used in this script are chosen based on appropriate theory on Linux to ensure the accuracy of output.
Any feedback or suggestions are most welcome!! 

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

Converting a file from uppercase to lowercase and vice-versa

Syntax to convert Upper to lowercase:

# dd if=[file with uppercase] of=[output filename] conv=lcase

[or]

# cat [file with uppercase] | tr '[:upper:]' '[:lower:]'  > output_file

Syntax to convert Lower to uppercase:

# dd if=[file with lowercase] of=[output filename] conv=ucase

[or]

# cat [file with lowercase] | tr '[:lower:]' '[:upper:]'  > output_file

How to check sudo access available for a Normal user ?

Lets say you logged into a Linux server as a Normal user and you want to know what sudo-access privileges your user-account has.

Run the command “sudo -l” to get the details about sudo-access (like shown below):

[ashok@hostxyz~]$ sudo -l
User ashok may run the following commands on this host:
(ALL) NOPASSWD: /bin/su - jboss
(ALL) NOPASSWD: /bin/su - nagios
(ALL) NOPASSWD: /bin/su – mysql
(ALL) /etc/init.d/postfix restart
(ALL) /etc/init.d/postfix start
(ALL) /etc/init.d/postfix stop
(ALL) /etc/init.d/httpd start
(ALL) /etc/init.d/httpd stop
[ashok@hostxyz~]$

Examining an unknown binary file in Linux

Scenario:  

Lets say you have come across an unknown Binary file in a Linux server and you want to know more details about it. 

Steps to follow:

i)    First run 'file' command to get its file-type and other details.

ii)   Check if the file is installed from any RPM by executing "rpm -qf  [filename]"

iii)  Check if the binary file uses any shared Library modules by running "ldd".

iv)  Check when was the file last modified and accessed, by using "stat" command.

v)   Finally check the printable characters in that file by using "strings" command and see if you could figure out anything from the output. "strings" output usually show the System calls made by that file and it will give you a clue about it. If you are familiar with "C" functions such as fopen, stdin, malloc etc, it would be relatively easier for you to figure out.  

Illustration:    

[root@hostxyz tmp]# ls

hsperfdata_root  lost+found  strange_file

[root@hostxyz tmp]# file strange_file

strange_file: ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV), for GNU/Linux 2.6.9, dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped

[root@hostxyz tmp]# rpm -qf strange_file

file /tmp/strange_file is not owned by any package

[root@hostxyz tmp]# ldd strange_file

        libproc-3.2.7.so => /lib64/libproc-3.2.7.so (0x0000003ea3000000)

        libc.so.6 => /lib64/libc.so.6 (0x0000003ea2c00000)

        /lib64/ld-linux-x86-64.so.2 (0x0000003ea2800000)

[root@hostxyz tmp]# stat strange_file

  File: `strange_file'

  Size: 7816            Blocks: 16         IO Block: 4096   regular file

Device: 803h/2051d      Inode: 98306       Links: 1

Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)

Access: 2011-07-28 16:52:03.000000000 -0500

Modify:  2011-07-28 15:48:20.000000000 -0500

Change: 2011-07-28 15:49:57.000000000 -0500

[root@hostxyz tmp]# strings strange_file

/lib64/ld-linux-x86-64.so.2

l$ L

usage: uptime [-V]

    -V    display version

libproc-3.2.7.so

__gmon_start__

_Jv_RegisterClasses

display_version

print_uptime

libc.so.6

stderr

fwrite

__libc_start_main

_3_2_5

GLIBC_2.2.5

/lib64/ld-linux-x86-64.so.2

[root@hostxyz tmp]#

Final note: Never open (vi) any binary file as it might corrupt it. Couple of times I had messed up some certification key file, which are in encrypted format.

How to find active TCP in Linux server ?

Situation:  You want to find all the Active TCP connections to a Linux machine for a given Port No. or a Port range. This you might want to do, to find any unauthorized access, to find the server utilization or for trouble-shooting purpose.


Solution:  Use 'lsof' or 'netstat' with appropriate switches. Here I illustrated about using 'lsof' as it will give more legible output when compare to 'netstat' command.


Syntax:  
# lsof -i @[Server IP]:[Port no or Port-no range] -R | grep TCP | sort -k7 -u


Example:
For demonstration purpose, I logged-in to a Linux FTP server and connected it from 3 remote servers via FTP protocol (port: 21).


Command to find how many FTP connections the server has now:
[root@ftpserver~]# lsof -i @10.20.64.30:21 -R | grep TCP | sort -k7 -u
vsftpd  12355 12353 adevaraju    0u  IPv4 58945888       TCP ftpserver:ftp->r3aash01-d1.prod.domain:44760 (ESTABLISHED)
vsftpd  12605 12602 adevaraju    0u  IPv4 58946864       TCP ftpserver:ftp->stoash01-t1.prod.domain:25559 (ESTABLISHED)
vsftpd  13191 13189 adevaraju    0u  IPv4 58947254       TCP ftpserver:ftp->gtwash01.prod.domain:50426 (ESTABLISHED)
[root@ftpserver ~]#


Command to find how many connections the server has in port range 20 - 80:
# lsof -i @10.20.64.30:20-80 -R | grep TCP | sort -k7 -u
[Output not shown]

PS: I have already written a post on using 'lsof' and 'netstat'. Please refer it as well:
http://ashok-linux-tips.blogspot.com/2010/10/how-to-pid-associated-with-port-no.html

Granting sudo access to reset local user-accounts password

In a RHEL server, I want to grant sudo access for a Group to reset any local User-accounts' password. At the same time, I don't want them to reset the password of ROOT user.

Solution:   Use ! (exclude) option in /etc/sudoers file.

Syntax:  %groupname ALL=(ALL) NOPASSWD: /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root

Refer this also:  http://ashok-linux-tips.blogspot.com/2010/09/using-wild-characters-while-providing.html