March 2023 - ILUG-D - lists.fsci.in

1D1C - test
by Dhanasekar 31 Mar '23

31 Mar '23

test - check file types and compare values To print “Yes, that’s true.” when 100 is greater than 99. $ test 100 -gt 99 && echo "Yes, that's true." || echo "No, that's false." To print "No, that's false." when 99 is greater than 100. $ test 99 -gt 100 && echo "Yes, that's true." || echo "No, that's false." To check if a file exists and is a regular file $ test -f /etc/resolv.conf && echo "File /etc/resolv.conf found." || echo "File /etc/resolv.conf not found." $ test -f /etc/ssh/sshd_config && echo "File /etc/ssh found." || echo "File /etc/ssh not found." To print 0 when the expression is true and two strings are identical. $ [ "awesome" = "awesome" ]; echo $? To print 1 when the expression is false and two strings are not identical. $ [ "awesome" = "1awesome" ]; echo $? To print "1" because the expression is false $ [ 7 -eq 10 ]; echo $? To print "0" because the expression is true $ [ 10 -eq 10 ]; echo $? regards, T.Dhanasekar

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1D1C - telnet
by Dhanasekar 30 Mar '23

30 Mar '23

telnet - is used for interactive communication with another host using the TELNET protocol $ telnet -l [username] [remote machine IP] [port (optional)] To connect to the device with specific IP address $ telnet 192.168.122.105 To quit the connected machine $ logout To connect remote server with user and port number $ telnet -l remote_user 192.168.122.105 3000 To connect to the telnet shell $ telnet telnet> To print help options $ telnet telnet > h To exit the telnet shell telnet > quit regards, T.Dhanasekar

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1D1C - telinit
by Dhanasekar 29 Mar '23

29 Mar '23

telinit - Change SysV runlevel syntax $ sudo telinit [options] {runlevel} To change the runlevel for a system without rebooting or changing the /etc/inittab $ sudo telinit 0 halt $ sudo telinit 1 single-user mode $ sudo telinit 2 Not used (user-definable) $ sudo telinit 3 Full multi-user mode $ sudo telinit 4 Not used (user-definable) $ sudo telinit 5 Full multi-user mode (with an X-based login screen) $ sudo telinit 6 Reboot $ sudo telinit q Reload daemon configuration equivalent systemctl daemon-reload regards, T.Dhanasekar

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1D1C - tcpdump
by Dhanasekar 26 Mar '23

26 Mar '23

tcpdump - prints out a description of the contents of packets on a network interface To capture packets from Specific Interface $ sudo tcpdump -i eth1 To capture only N number of packets $ sudo tcpdump -c 4 -i eth1 To display the package in ASCII format $ sudo tcpdump -A -i eth1 To Display Available Interfaces $ sudo tcpdump -D To Display Captured Packets in HEX and ASCII $ sudo tcpdump -XX -i eth1 To capture and save packets in a file $ sudo tcpdump -w 0002.pcap -i eth1 To read captured packets file $ sudo tcpdump -r 0002.pcap To capture IP address packets $ sudo tcpdump -n -i eth1 To capture only TCP packets. $ sudo tcpdump -i eth1 tcp To capture packet from specific port $ sudo tcpdump -i eth1 port 22 To capture packets from source IP $ sudo tcpdump -i eth1 src 192.168.122.50 To capture packets from destination IP $ sudo tcpdump -i eth1 dst 192.168.122.100 regards, T.Dhanasekar

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1D1C - tar
by Dhanasekar 25 Mar '23

25 Mar '23

tar - an archiving utility syntax $ tar <options> <files> To create an archive file $ tar -cvf myfile.txt /home/ilugc/ To create tar.gz Archive File $ tar cvzf mydoc.tar.gz /home/ilugc/Documents To create tar.bz2 archive file $ tar cvfj mydownloads.tar.bz2 /home/ilugc/Downloads To untar tar Archive file $ tar -xvf mydoc.tar To untar tar archive file in different location $ tar -xvf mydoc.tar -C /home/ilugc/Music/ To uncompress tar.gz Archive File $ tar -xvf mydoc.tar.gz To Uncompress tar.bz2 Archive File $ tar -xvf mydownloads.tar.bz2 To list Content of tar Archive File $ tar -tvf mydoc.tar To List Content tar.gz Archive File $ tar -tvf mydoc.tar.gz To List Content tar.bz2 Archive File $ tar -tvf mydownloads.tar.bz2 To Untar Single file from tar File $ tar -xvf files.sh.tar file.sh To Untar Single file from tar.gz File $ tar -zxvf backup.tar.gz backup.html To Untar Single file from tar.bz2 File $ tar -jxvf Python.tar.bz2 demo.py To Untar Multiple files from tar, tar.gz, and tar.bz2 File $ tar -xvf file.tar "file1" "file2" "file3" $ tar -zxvf myfile.tar.gz "file1" "file2" "file3" $ tar -jxvf myfiles.tar.bz2 "file1" "file2" "file3" To Extract Group of Files using Wildcard $ tar -xvf Python.tar --wildcards '*.py' $ tar -zxvf Perl.tar.gz --wildcards '*.pl' $ tar -jxvf Bash.tar.bz2 --wildcards '*.sh' To add files or directories to the existing tar archive files $ tar -rvf file.tar file.txt $ tar -rvf file.tar demo.py To Add Files or Directories to tar.gz and tar.bz2 Files $ tar -rvf file.tar.gz sample.txt $ tar -rvf Php.tar.bz2 sample.php To verify any tar or compressed archive file $ tar tvfW sample.tar To Check the Size of the tar, tar.gz, and tar.bz2 Archive File $ tar -czf - sample.tar | wc -c $ tar -czf - mydocs.tar.gz | wc -c $ tar -czf - mydownloads.tar.bz2 | wc -c To Exclude Files and Directories When Creating Tar File $ tar --exclude='example.txt' -zcvf file.tar.gz /home/ilugc $ tar --exclude='/home/ilugc/songs' -zcvf backup.tar.gz /home/ilugc To exclude files with specific file extensions when creating a tar archive file, $ tar --exclude='*.txt' -zcvf backup.tar.gz /home/ilugc $ tar --exclude='*.py' -zcvf backup.tar.gz /home/ilugc To remove File and Directory from Tar Archive $ tar --delete -f backup.tar.gz sample.txt $ tar --delete -f backup.tar.gz '/home/tecmint/songs' To extract Specific File Extension in Tar Archive $ tar -xvf backup.tar.gz --wildcards '*.mp4' regards, T.Dhanasekar

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1D1C - taskset
by Dhanasekar 24 Mar '23

24 Mar '23

taskset - is used to set or retrieve the CPU affinity of a running process To fetch the CPU Affinity of a Process $ pidof sshd $ taskset -p <PID_of_sshd> To get the CPU range of a process $ taskset -cp <PID_of_sshd> To change the CPU affinity of a process by assigning the new value to the PID of the existing process $ taskset -p 0x7 <PID_of_sshd> To Change CPU range $ taskset -cp 0,2 <PID_of_sshd> To set the CPU core $ taskset -c 3,5 sshd $ taskset -c 0-4 sshd regards, T.Dhanasekar

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1D1C - tail
by Dhanasekar 23 Mar '23

23 Mar '23

tail - output the last part of files To display the last 10 lines of a file $ tail /var/log/messages To Display the last N lines in a file $ tail -n 4 /var/log/messages To Print filename header $ tail -v example.txt $ tail -v /var/log/messages To Display the last n lines from multiple files $ tail -n 4 file1.txt file2.txt $ tail -n 4 /var/log/messages /var/log/apache2/access.log To Save the output of tail command to a text file $ tail -n 10 /var/log/apache2/access.log > output.txt To append to output.txt $ tail -n 10 /var/log/messages >> output.txt To monitor real-time log files $ tail -f /var/log/messages To use pipes $ tail -file.txt | sort $ tail /var/log/messages | sort $ tail /var/log/messages | tail -n 6 | sort To Print N number of bytes data from a file $ tail -c 500 /var/log/messages $ tail -c 10M /var/log/messages To print help options $ tail --help regards, T.Dhanasekar

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1D1C - tac
by Dhanasekar 22 Mar '23

22 Mar '23

tac - is used to concatenate and print files in reverse syntax $ tac [OPTION]... [FILE]... $ cat example.txt This is line 1 This is line 2 This is line 3 This is line 4 This is line 5 $ cat example1.txt This is msg 1 This is msg 2 This is msg 3 This is msg 4 This is msg 5 To print files in reverse $ tac example.txt To attach the separator before instead of after $ tac -b example.txt example1.txt To make the STRING as the separator $ tac --separator="STRING" example1.txt example.txt To interpret the separator as a regular expression $ tac -r example.txt example1.txt regards, T.Dhanasekar

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1D1C - systemd-machine-id-setup
by Dhanasekar 21 Mar '23

21 Mar '23

systemd-machine-id-setup - Initialize the machine ID in /etc/machine-id To clear the original “machine-id” $ sudo rm /etc/machine-id To create the new “machine-id” value $ sudo systemd-machine-id-setup To verify the new value of machine-id. $ cat /etc/machine-id regards, T.Dhanasekar

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1D1C - systemd-analyse
by Dhanasekar 20 Mar '23

20 Mar '23

systemd-analyse - Analyze and debug system manager To determine system boot-up performance statistics $ systemd-analyze To Print time required to boot the machine $ systemd-analyze time To Print list of running units ordered by time to init $ systemd-analyze blame To Print a tree of the time critical chain of units $ systemd-analyze critical-chain Output state serialization of service manager $ systemd-analyze dump Output SVG graphic showing service initialization $ systemd-analyze plot To List load directories for units $ systemd-analyze unit-paths To List exit status definitions $ systemd-analyze exit-status To Analyze security of unit $ systemd-analyze security regards, T.Dhanasekar

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ILUG-D March 2023