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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

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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

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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

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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

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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

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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

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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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