- ILUG-D - lists.fsci.in

1D1C - ssh-keygen
by Dhanasekar 05 Mar '23

05 Mar '23

ssh-keygen - is used to generate a public/private authentication key pair To generate ssh key without any arguments $ ssh-keygen To define key type $ ssh-keygen -t rsa $ ssh-keygen -t dsa To define bit size default is 2048 $ ssh-keygen -b 4096 To assign passphrase $ ssh-keygen -P "myp@ssword" To change passphrase of the private key $ ssh-keygen -p To create keys with custom filename $ ssh-keygen -f my-rsa-key To add custom comment to the key $ ssh-keygen -C "This key is for my.server.in" To change comment of the key $ ssh-keygen -c To hash the content of known_hosts file $ ssh-keygen -H To delete all the keys related to 192.168.122.101 host from known_hosts file $ ssh-keygen -R 192.168.122.101 regards, T.Dhanasekar

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1D1C - sshd
by Dhanasekar 04 Mar '23

04 Mar '23

sshd - is the daemon program for ssh To use either IPv4 or IPv6 only # /usr/sbin/sshd -4 # /usr/sbin/sshd -6 To display debug modes # /usr/sbin/sshd -D # /usr/sbin/sshd -d -d -d To send the error messages to the standard error # /usr/sbin/sshd -d -e To use own config file for sshd apart default /etc/ssh/sshd_config # /usr/sbin/sshd -f /root/conf/custom_sshd.conf To customize SSHD grace time # /usr/sbin/sshd -g 180 To specify options in command line # /usr/sbin/sshd -o "AllowUsers user3 user4" regards, T.Dhanasekar

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1D1C - ssh-copy-id
by Dhanasekar 03 Mar '23

03 Mar '23

ssh-copy-id - use locally available keys to authorise logins on a remote machine create ssh key $ ssh-keygen -t rsa To copy ssh key to remote machine $ ssh-copy-id -i /home/ilugc/.ssh/id_rsa.pub user(a)192.168.122.101 To enable forced mode to copy ssh key to remote machine $ ssh-copy-id -f -i /home/dhana/.ssh/id_rsa.pub dhana(a)192.168.122.101 To perform dry-run that prints the keys intended for installation without installing them on the remote host $ ssh-copy-id -n -i /home/dhana/.ssh/id_rsa.pub dhana(a)192.168.122.101 To connect to a remote host when the default SSH port is not being used. $ ssh-copy-id -i -p <custom_port> /home/dhana/.ssh/id_rsa.pub dhana(a)192.168.122.101 regards, T.Dhanasekar

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1D1C - ssh-agent
by Dhanasekar 02 Mar '23

02 Mar '23

ssh-agent - is a program to hold private keys used for public key authentication To start the ssh-agent $ ssh-agent To stop / kill the ssh-agent $ ssh-agent -k To run ssh-agent in debug mode $ ssh-agent -d To set bind socket name $ ssh-agent -a ~/demo-ssh-socket $SHELL To set expiry time for keys $ ssh-agent -t 1800 $SHELL $ ssh-agent -t 10D $SHELL regards, T.Dhanasekar

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1D1C - ssh-add
by Dhanasekar 01 Mar '23

01 Mar '23

ssh-add - adds private key identities to the OpenSSH authentication agent To create the public key and the private key $ ssh-keygen -t rsa To keep the identity of the agents for 600 seconds. $ ssh-agent -t 600 To make ssh-agent command for non-interactive authentication $ eval $(ssh-agent) To add the private key passphrase to ssh-agent $ ssh-add To list my private keys cached by ssh-agent $ ssh-add -l To list all public key parameters of all identities $ ssh-add -L To remove all cached ssh-agent private keys $ ssh-add -D To lock the SSH Agent $ ssh-add -x To unlock SSH Agent $ ssh-add -X regards, T.Dhanasekar

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1D1C - ssh
by Dhanasekar 28 Feb '23

28 Feb '23

ssh - is a program for logging into a remote machine and for executing commands on a remote machine To access remote server $ ssh 192.168.122.50 $ ssh my.server.in To specify a username for SSH connection $ ssh username@hostname_or_ip $ ssh -l username@hostname_or_ip $ ssh -l user1(a)192.168.122.50 $ ssh -l user1(a)my.server.in To use a different port number for ssh connection $ ssh my.server.in -p 2222 $ ssh 192.168.122.50 -p 2222 To run a command on a remote server from a local computer $ ssh 192.168.122.50 rm ~/Desktop/test_file.txt To execute multiple commands using SSH on remote nodes $ ssh 192.168.122.50 command1; command2; command3 To make ssh to use protocol version 2 $ ssh -2 user1(a)192.168.122.50 To Print debug information $ ssh -v user1(a)192.168.122.50 To increase the level of verbosity $ ssh -vv user1(a)192.168.122.50 To get more level of verbosity $ ssh -vvv user1(a)192.168.122.50 To enable X11 forwarding with ssh command $ ssh -X ip_address $ ssh -X 192.168.122.50 To hide the error message $ ssh -q 192.168.122.50 To change any default value to other possible values during ssh $ ssh -o option=value ip_address $ ssh -o Port=2222 192.168.122.50 regards, T.Dhanasekar

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1D1C - ss
by Dhanasekar 27 Feb '23

27 Feb '23

ss - is used to dump socket statistics, and to investigate sockets To list all Connections $ ss To list Listening and Non-listening Ports $ ss -a To list Listening Sockets $ ss -l To list all TCP connections $ ss -t To list all listening TCP connections $ ss -lt To list all UDP connections $ ss -ua To list all listening UDP connections $ ss -lu To display PID of sockets $ ss -p To display summary statistics $ ss -s To display IPv4 and IPv6 socket connections $ ss -4 $ ss -6 To filter connections by port number $ ss -at '( dport = :22 or sport = :22 )' $ ss -at '( dport = :80 or sport = :80 )' $ ss -at '( dport = :ssh or sport = :ssh )' $ ss -at '( dport = :http or sport = :http )' regards, T.Dhanasekar

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computer spares/ parts
by PETER REGELOUS 26 Feb '23

26 Feb '23

Hi Mr Dhanasekar Nice to e-meet Are these items of use I have found 1 man who is gifting them! @ , motherboard, cooler, RAM , graphics cards , laptop PSU, 5v 9v 12v power bricks, modem What can we use these for ? Kind regards @ ukX Peter Regelous

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1D1C - split
by Dhanasekar 26 Feb '23

26 Feb '23

split - is used to split large files into smaller files syntax $ split {options} {file_name} {prefix} $ cat example.txt This is line 1 This is line 2 This is line 3 This is line 4 This is line 5 This is line 6 This is line 7 This is line 8 This is line 9 This is line 10 To split example.txt with verbose option $ split example.txt --verbose To split files with customize line numbers $ split -l5 example.txt --verbose To split files with file size $ split -b 4 example.txt --verbose (in bytes) $ split -b 2K <file_name> --verbose (in Kb) $ split -b 2M <file_name> --verbose (in Mb) $ split -b 1G <file_name> --verbose (in Gb) To create Split files with numeric suffix instead of alphabetic $ split -d example.txt --verbose x00 To split file with customize suffix $ split -l5 example.txt ilugc_file To generate n chunks output files $ split -n5 <file_name> To Prevent Zero Size Split output files $ split -n60 -e example.txt To create split output files of customize suffix length $ split -b 4 example.txt -a 3 $ split -b 4 example.txt -a 4 To split ISO file and merge it into a single file $ split -n5 ubuntu-22.04.iso Split_IS0_ it will split ISO file into 5 pieces To merge these files into a single $ cat Split_IS0_a* > ubuntu22.04_new.iso To verify the integrity of merge file using md5sum before split of iso $ md5sum ubuntu22.04.iso after split and merge $ md5sum ubuntu22.04_new.iso regards, T.Dhanasekar

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1D1C - source
by Dhanasekar 25 Feb '23

25 Feb '23

source - is a built-in shell command that reads and executes the file content in the current shell. syntax $ source [filename] [arguments] To pass commands and arguments $ cat example.txt free -h pwd date time uptime $ source example.txt To read variables from a file $ cat example.sh #!/bin/bash VAR1="a" VAR2="b" VAR3="c" create bash script $ cat sample.sh #!/bin/bash source example.sh echo "VAR1 is $VAR1" echo "VAR2 is $VAR2" echo "VAR3 is $VAR3" $ source sample.sh To refresh the current shell environment $ alias ll = 'ls -l' $ alias c = 'clear' $ c $ ll This command only works in the current shell session To make it permanent $ sudo nano ~/.bashrc alias ll = 'ls -l' alias c = 'clear' :x Refresh the current shell environment and make it permanent for the user $ source ~/.bashrc To make it system wide change $ sudo vim /etc/profile alias ll = 'ls -l' alias c = 'clear' :x # source /etc/profile regards, T.Dhanasekar

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