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

1D1C - strace
by Dhanasekar 09 Mar '23

09 Mar '23

strace - is a CLI tool for debugging and troubleshooting programs To trace of all system calls made command free -h $ strace free -h $ strace df -Th To Trace Linux Process PID $ sudo strace -p <PID> To get summary of linux process $ sudo strace -c -p <PID> To Print Instruction Pointer During System Call $ sudo strace -i df -Th $ sudo strace -i free -h To show Time of Day For Each Trace Output Line $ sudo strace -t df -Th $ sudo strace -t free -h To Print Command Time Spent in System Calls $ sudo strace -T df -Th $ sudo strace -T free -h To trace Only Specific System Calls $ sudo strace -e trace=write df -Th $ sudo strace -e trace=write free -h $ sudo strace -e trace=all df -Th $ sudo strace -e trace=all free -h To trace System Calls Based on a Certain Condition To trace all system calls involving process management $ sudo strace -q -e trace=process df -Th $ sudo strace -q -e trace=process free -h To trace all system calls that take a filename as an argument, $ sudo strace -q -e trace=file df -Th $ sudo strace -q -e trace=file free -h To trace all system calls involving memory mapping $ sudo strace -q -e trace=memory df -Th $ sudo strace -q -e trace=memory free -h To redirect Trace Output to File $ sudo strace -o df_debug.txt df -Th $ sudo strace -o free_debug.txt free -h To show debugging information for strace $ strace -d df -Th $ strace -d free -h regards, T.Dhanasekar

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1D1C - stat
by Dhanasekar 08 Mar '23

08 Mar '23

stat - display file or file system status To view the file details $ stat example.txt To view information about multiple files $ stat sample.pdf example.txt To display file system status $ stat -f /home To display information in terse form $ stat -t sample.pdf $ stat -t example.txt $ stat -t sample.pdf example.txt To enable following of symbolic links $ stat /usr/share/zoneinfo/Asia/Calcutta To get information on the file that the links points $ stat -L /usr/share/zoneinfo/Asia/Calcutta To format sequencing To display inode of a file only $ stat --printf='%i\n' example.txt To display access rights and uid (User ID) $ stat --printf='%a:%u\n' example.txt To print out a new line without requiring an additional operand. $ stat --format='%a:%F' example.txt To display help options $ stat --help regards, T.Dhanasekar

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1D1C - startx
by Dhanasekar 07 Mar '23

07 Mar '23

startx command launches an X11 session. To start an X session at 16 bits color depth. $ startx -- -depth 16 To start an X session at 100 dpi (dots per inch) resolution. $ startx -- -dpi 100 To start an X session with support for multiple displays. $ startx -- -layout Multihead regards, T.Dhanasekar

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1D1C - ssh-keyscan
by Dhanasekar 06 Mar '23

06 Mar '23

ssh-keyscan - is a utility for gathering the public SSH host keys of a number of hosts To read all public keys from the host $ ssh-keyscan 192.168.122.50 To read all public keys from the host at port number 22 $ ssh-keyscan -p 22 192.168.122.50 To read all public keys of the rsa type $ ssh-keyscan -t rsa 192.168.122.50 To update the known_hosts file located in the path, ~/.ssh/known_hosts $ ssh-keyscan -H 192.168.122.50 >> ~/.ssh/known_hosts regards, T.Dhanasekar

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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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ILUG-D March 2023