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

1D1C - systemd
by Dhanasekar 19 Mar '23

19 Mar '23

systemd - is a system and service manager for Linux operating systems To find boot process duration $ systemd-analyze $ systemd-analyze time To analyze time taken by each process at boot $ systemd-analyze blame To analyze critical chain at boot $ systemd-analyze critical-chain To Determine the initial start-up transaction $ systemd --test To make not to pipe output into a pager $ systemd --test --no-pager To Dump understood unit configuration items $ systemd --dump-configuration-items To dump exposed bus properties $ systemd --dump-bus-properties regards, T.Dhanasekar

1 0

1D1C - systemctl
by Dhanasekar 18 Mar '23

18 Mar '23

systemctl - Control the systemd system and service manager syntax $ systemctl [OPTION] [SERVICE] To start service $ sudo systemctl start mariadb.service $ sudo systemctl start sshd To stop service $ sudo systemctl stop mariadb.service $ sudo systemctl stop sshd To restart or reload service $ sudo systemctl reload mariadb.service $ sudo systemctl restart mariadb.service To reload a service default, but if reload is not available for that service. It will restart it $ sudo systemctl reload-or-restart mariadb.service To check status of service $ sudo systemctl status mariadb.service $ sudo systemctl status sshd To enable service $ sudo systemctl enable mariadb.service $ sudo systemctl enable sshd To disable service $ sudo systemctl disable mariadb.service $ sudo systemctl disable sshd To check Service is enabled or disabled $ sudo systemctl is-active mariadb.service $ sudo systemctl is-active sshd $ sudo systemctl is-enabled mariadb.service $ sudo systemctl is-enabled sshd To see the status of all services $ sudo systemctl list-units --type=service To List services by status $ sudo systemctl list-units --type=service --state=active $ systemctl list-units --type=service --state=running $ systemctl list-units --type=service --state=stopped $ systemctl list-units --type=service --state=enabled $ systemctl list-units --type=service --state=disabled $ systemctl list-units --type=service --state=failed To prevent service from starting $ sudo systemctl mask {servicename} To Kill a service with signal 15 $ sudo systemctl kill {servicename} To Kill a service with signal 9 $ sudo systemctl kill -s 9 {servicename} To Reboot $ sudo systemctl reboot To shutdown $ sudo systemctl poweroff To change default to GUI $ sudo systemctl set-default graphical.target To switch to multi-user.target $ sudo systemctl isolate multi-user.target To reload daemon $ systemctl daemon-reload To find version $ systemctl --version regards, T.Dhanasekar

1 0

1D1C - sysctl
by Dhanasekar 17 Mar '23

17 Mar '23

sysctl - configure kernel parameters at runtime To view all current kernel parameters invoke the sysctl $ sudo sysctl -a To view the swappiness value $ sudo sysctl vm.swappiness $ sysctl kernel.hostname To Modify the Kernel Parameters $ sudo sysctl -w parameter=value To enable IPv4 packet forwarding $ sudo sysctl -w net.ipv4.ip_forward=1 To set a parameter permanently $ sudo sysctl -w net.ipv4.ip_forward=1 >> /etc/sysctl.conf To read values from file $ sudo sysctl -p /etc/sysctl.d/file_name.conf To print variable names without values $ sudo sysctl -N vm.swappiness To print values only of the given variable $ sudo sysctl -n vm.swappiness To read values from all system directories $ sudo sysctl --system To print version and help options $ sudo sysctl --version $ sudo sysctl --help regards, T.Dhanasekar

1 0

1D1C - sync
by Dhanasekar 16 Mar '23

16 Mar '23

sync - is used to synchronize the data of the temporary memory to the permanent storage memory syntax $ sync [option] [file] To sync all the cached files to the permanent memory which belongs to the current user $ sudo sync To sync only file data, no unneeded metadata $ sudo sync -d /home/ilugc/file1.txt To sync all the files in dir $ sudo sync -f /home/ilugc/Downloads To sync the cache data of the mounted partition $ sudo sync /dev/vda1 $ sudo sync /var/log/syslog regards, T.Dhanasekar

1 0

1D1C - swapon
by Dhanasekar 15 Mar '23

15 Mar '23

swapon - enable devices and files for paging and swapping syntax $ swapon <option> To enable all swap devices and files listed in the /etc/fstab $ sudo swapon -a $ sudo swapon -av To enable swap device with device name $ sudo swapon -a /dev/vda5 $ sudo swapon -av /dev/vda5 To display the swap usage summary of all enabled swap devices and files $ sudo swapon -s To enable the swap discards if the device supports the discard operation $ sudo swapon -d To reinitialize the swap space $ sudo swapon -f To display a summary table with selected columns $ swapon --show=NAME,SIZE To print the raw output format $ sudo swapon --raw regards, T.Dhanasekar

1 0

1D1C - swapoff
by Dhanasekar 14 Mar '23

14 Mar '23

swapoff - disables swapping on the specified devices and files To deactivate the swap $ sudo swapoff /dev/vda5 $ sudo swapoff -v /dev/vda5 To disable all swaps from /proc/swaps $ sudo swapoff -a $ sudo swapoff -av To check if the swap area has been disabled $ free -h or $ sudo swapon --show regards, T.Dhanasekar

1 0

1D1C - swaplabel
by Dhanasekar 13 Mar '23

13 Mar '23

swaplabel - print or change the label or UUID of a swap area To print the swaplabel $ sudo swaplabel /dev/vda5 To change the swaplabel, first make swapoff $ sudo swapoff -a then, change the swaplabel name $ sudo swaplabel -L mynewswap /dev/vda5 then, $ sudo swapon -a check with $ sudo swapon --show now new swaplabel is fixed $ sudo swaplabel /dev/vda5 regards, T.Dhanasekar

1 0

1D1C - sudo
by Dhanasekar 12 Mar '23

12 Mar '23

sudo - allows a permitted user to execute a command as the superuser or another user To run command as a root user $ sudo <command> $ sudo pwd To run command as a different user $ sudo -u user3 <command> $ sudo -u user3 pwd To List user privileges with sudo $ sudo -l To Display privileges for another user with sudo $ sudo -l -U user3 To add a user to the sudo group $ sudo usermod -aG sudo user3 To add users to the sudoers file $ sudo visudo To run command in the background $ sudo -b <command> To update sudoers files $ sudo -e <file> To update the user’s cached credentials $ sudo -v To invalidate user’s cached credentials $ sudo -k regards, T.Dhanasekar

1 0

1D1C - su
by Dhanasekar 11 Mar '23

11 Mar '23

su - run a command with substitute user and group ID su command without any option $ su su command to make the shell a login shell $ su - user3 To switch to root user $ su - To print help options $ su -h To switch to a Different User $ su -l user3 To Use su with sudo command $ sudo su - user3 To run specific command as a different user $ su -c pwd user3 To use a different shell $ su -s /usr/bin/csh To Execute a command as different user with su command $ su -c <command> user3 To use a different user in the same environment $ su -p user3 $ su -m user3 regards, T.Dhanasekar

1 0

1D1C - strip
by Dhanasekar 10 Mar '23

10 Mar '23

strip - discard symbols and other data from object files syntax $ strip [options] objfile... $ cat hello.c #include <stdio.h> int main() { // printf() displays the string inside quotation printf("Hello, World!"); return 0; } $ gcc hello.c -o hello.out To strip the symbol table $ readelf -s hello.out $ strip -s hello.out check the symbol table $ readelf -s hello.out To remove debug symbols only $ strip --strip-debug hello.out check the symbol table $ readelf -a hello.out To Remove a particular section $ readelf -S hello.out strip the .gnu.version section from the executable $ strip -R .gnu.version hello.out check the list of sections $ readelf -S hello.out To Remove unneeded symbols $ strip --strip-unneeded hello.out $ readelf -a hello.out To Shield a particular symbol from stripping $ strip -s -K hello.c hello.out $ readelf -s hello.out To strip off a particular symbol $ strip -N hello.c hello.out $ readelf -s hello.out To create a new stripped off file $ strip -s -o stripped_hello hello.out $ ls -lart stripped_hello To preserve the access and modification date/time check the access and modification time of the original file $ stat hello.out $ strip -s -p hello.out regards, T.Dhanasekar

1 0

2024

2023

2022

2021

ILUG-D March 2023