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

1D1C - lvcreate / lvs / lvdisplay / lvremove
by Dhanasekar 18 Sep '23

18 Sep '23

lvcreate - Create a Logical Volume in an existing Volume Group. To create logical volume my_vol in an existing volume group myvol_grp # lvcreate --size 500M --name my_vol vol_grp To report logical volume info # lvs To report all logical volume # lvs --all To shows the information of all logical volumes # lvdisplay To display information of a specific logical volume # lvdisplay /path/to/lv To display output in columns # lvdisplay -C To display the mapping of logical extents to physical volumes and physical extents. # lvdisplay --maps To display all the information # lvdisplay -a To remove the logical volume # lvremove path/to/lv To forcefully remove active logical volumes # lvremove -f /path/to/lv regards, T.Dhanasekar

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1D1C - vgremove
by Dhanasekar 17 Sep '23

17 Sep '23

vgremove - Remove a Volume Group To remove a volume group name myvol_grp # vgremove vol_grp regards, T.Dhanasekar

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1D1C - vgcreate / vgdisplay / vgrename / vgs
by Dhanasekar 16 Sep '23

16 Sep '23

vgcreate - Create a Volume Group To create a volume group named vg00 using /dev/sdb and /dev/sdc # vgcreate vg00 /dev/sdb /dev/sdc To Display attributes of Volume Groups # vgdisplay vg00 To rename the name of a volume group # vgrename vg00 demovg To display information about volume groups # vgs To display all volume groups # vgs -a To show more details # vgs -v regards, T.Dhanasekar

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1D1C - pvscan
by Dhanasekar 15 Sep '23

15 Sep '23

pvscan - Scan all disks for Physical Volumes To scan all disks for physical volumes # pvscan To print physical volumes belonging to exported volume groups # pvscan -e To display short listing format # pvscan -s To Show UUIDs # pvscan -u To set to verbose mode # pvscan -v regards, T.Dhanasekar

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1D1C - pvremove
by Dhanasekar 14 Sep '23

14 Sep '23

pvremove - Remove a Physical Volume To remove a physical volumes # pvremove /dev/sdb To set to debug mode # pvremove -d /dev/sdb To force the pv remove # pvremove -f /dev/sdb To test the pvremove # pvremove -t /dev/sdb To set to verbose mode # pvremove -v /dev/sbd To get the pvremove help # pvremove --help regards, T.Dhanasekar

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1D1C - pvresize
by Dhanasekar 13 Sep '23

13 Sep '23

pvresize - Resize a disk or partition in use by LVM2 To adjust the size of the physical volume /dev/sdb # pvresize /dev/sdb To resize a physical volume, by reducing it # pvresize --setphysicalvolumesize 20G /dev/sdb To set to debug mode # pvresize -d To run pvresize in test mode # pvresize -t /dev/sdb To set to verbose mode # pvresize -v To get the help for pvresize # pvresize --help regards, T.Dhanasekar

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1D1C - pvcreate
by Dhanasekar 12 Sep '23

12 Sep '23

pvcreate - Initialize physical volume(s) for use by LVM To create physical volumes on top of /dev/sdb, /dev/sdc # pvcreate /dev/sdb /dev/sdc To report information about Physical Volumes # pvs To display attributes of a Physical Volume # pvdisplay /dev/sdb # pvdisplay /dev/sdc regards, T.Dhanasekar

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1D1C - lvm
by Dhanasekar 11 Sep '23

11 Sep '23

lvm - it provides tools to create virtual block devices from physical devices To start the Logical Volume Manager interactive shell $ lvm lvm> To view the config $ sudo lvm config To display the recognised built-in block device types $ sudo lvm devtypes To view the dumpconfig $ sudo lvm dumpconfig To display recognised metadata formats $ lvm > formats To display information about PVs, PV segments, VGs, LVs and LV segments, all at once $ sudo lvm fullreport To print help options $ sudo lvm help To display log report of last command run in LVM shell if command log reporting is enabled $ sudo lvm lastlog To Display recognised Logical Volume segment types $ sudo lvm segtypes To display version information $ lvm version regards, T.Dhanasekar

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1D1C - journalctl
by Dhanasekar 10 Sep '23

10 Sep '23

journalctl - Query the systemd journal To display all logs $ journalctl To display the new entries first in logs $ journalctl -r To display a specific number of log entries $ journalctl -n 5 To retrieve log entries containing a specific keyword $ journalctl | grep <keyword> $ journalctl | grep nginx $ journalctl | grep apache2 To display log entries based on their priority level $ journalctl -p warning To display verbose output $ journalctl -o verbose To view information about previous system boots $ journalctl --list-boots To print help options $ journalctl --help regards, T.Dhanasekar

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1D1C - update-alternatives
by Dhanasekar 09 Sep '23

09 Sep '23

update-alternatives - maintain symbolic links determining default commands To check for the version update-alternatives $ update-alternatives --version To choosing the Alternative in Manual Mode With config for editors $ sudo update-alternatives --config editor To choose the alternative with set $ sudo update-alternatives --list editor /bin/ed /bin/nano /usr/bin/vim.basic /usr/bin/vim.tiny To choose and set manually vim.basic editor $ sudo update-alternatives --set editor /usr/bin/vim.basic To set back to auto mode $ sudo update-alternatives --auto editor Adding New Alternative With install $ sudo apt install emacs To make emacs editor available in editor options and set 100 as priority $ sudo update-alternatives --install /usr/bin/editor editor /usr/bin/emacs 100 $ /usr/bin/editor will make open emacs as default editor To list alternatives with get-selections $ sudo update-alternatives --get-selections regards, T.Dhanasekar

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1D1C - avcstat
by Dhanasekar 08 Sep '23

08 Sep '23

avcstat - Display SELinux AVC statistics To print short output of the access vector cache statistics since boot $ sudo avcstat To show output at one second interval $ sudo avcstat 1 To show output at 5 seconds interval $ sudo avcstat 5 regards, T.Dhanasekar

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1D1C - chronyc
by Dhanasekar 07 Sep '23

07 Sep '23

chronyc - is a command-line utility for managing and monitoring the chrony daemon, which is a daemon that provides network time synchronization on Linux systems To display the status of the chrony daemon $ chronyc tracking To start chronyc in interactive mode $ chronyc chronyc> To print the time sources that Chrony is currently using $ chronyc sources To display stats for sources currently used by chrony daemon as a time source $ chronyc sourcestats To display verbose information about each NTP source $ sudo chronyc ntpdata regards, T.Dhanasekar

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1D1C - rpmquery
by Dhanasekar 06 Sep '23

06 Sep '23

rpmquery - is used to query package information from the RPM database To display information about a specific package $ sudo rpmquery vsftpd $ sudo rpmquery httpd To display information about multiple packages $ sudo rpmquery vsftpd httpd bind To display the version number of a package $ sudo rpmquery -q httpd To display the files that are included in a package $ sudo rpmquery --list bind $ sudo rpmquery --list httpd To display the architecture of a package $ sudo rpmquery --queryformat '%{ARCH}\n' httpd regards, T.Dhanasekar

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1D1C - rpmverify
by Dhanasekar 05 Sep '23

05 Sep '23

rpmverify - verifies the correctness of installed RPM packages To verify the correctness of the vsftpd , httpd package $ rpmverify vsftpd $ rpmverify httpd To verify all installed packages $ rpmverify -a regards, T.Dhanasekar

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1D1C - semodule
by Dhanasekar 04 Sep '23

04 Sep '23

semodule - Manage SELinux policy modules To view the policy module loaded by SELinux $ sudo semodule -l To view the apache policy module $ sudo semodule -l | grep apache To disable the zabbix policy module $ sudo semodule -d zabbix regards, T.Dhanasekar

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1D1C - firewall-offline-cmd
by Dhanasekar 03 Sep '23

03 Sep '23

firewall-offline-cmd - firewalld offline command line client It should be used only if the firewalld service is not running To add a port to firewall daemon when firewalld is offline $ sudo firewall-offline-cmd --port=80:tcp $ sudo firewall-offline-cmd --port=443:tcp $ sudo firewall-offline-cmd --port=3306:tcp To remove a port to firewall daemon when firewalld is offline $ sudo firewall-offline-cmd --remove-port=80:tcp $ sudo firewall-offline-cmd --remove-port=443:tcp $ sudo firewall-offline-cmd --remove-port=3306:tcp $ sudo firewall-offline-cmd --remove-port=53:tcp To list all the ports under all the zones $ sudo firewall-offline-cmd --list-all regards, T.Dhanasekar

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1D1C - PS1
by Dhanasekar 02 Sep '23

02 Sep '23

PS1 - is the current bash shell prompt To display current bash shell prompt setting $ echo $PS1 To print the current settings from your ~/.bashrc $ grep PS1 ~/.bashrc To customise the bash prompt to ilugc > temporarily $ PS1="\e[1;32milugc> \e[m" To display customised colours for bash prompt $ PS1="\e[1;32milugc> \e[m" $ PS1="\e[1;33milugc> \e[m" $ PS1="\e[1;35milugc> \e[m" $ PS1="\e[1;36milugc> \e[m" $ PS1="\e[1;37milugc> \e[m" $ PS1="\e[1;38milugc> \e[m" To make the above bash prompt permanently $ vim ~/.bashrc comment the old entries with PS1 then add the entry PS1="\e[1;32milugc> \e[m" : wq! save and exit then $ source ~/.bashrc To make system wide $ sudo vim /etc/profile comment the old entries with PS1 then add the entry PS1="\e[1;32milugc> \e[m" : wq! save and exit then # source /etc/profile To set emoji in bash prompt $ PS1="\e[1;32milugc🎄 \e[m" PS1="\e[1;32milugc🦌 \e[m" regards, T.Dhanasekar

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1D1C - set
by Dhanasekar 01 Sep '23

01 Sep '23

set - is used to set and unset certain flags or settings within the shell environment syntax $ set [options] To display a list of all system settings $ set To print help options $ set --help To turn on the debugging information in a shell script $ set -x To turn off the debugging information $ set +x To disable the default behavior of Bash $ set -C To stop a script immediately $ set -e regards, T.Dhanasekar

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ILUG-D September 2023