Useful ubuntu commands

Traceroute utility

For troubleshooting ip reachability

apt-get install trace route

Troubleshoot

What to do if you see reboot is delayed with log "a start job is running for raise network interfaces"

It happened to me when an interface was configured for DHCP. Check /etc/network/interfaces if any interface is configured for DHCP.

Useful link:

https://askubuntu.com/questions/773973/ubuntu-16-04-system-boot-waits-saying-raise-network-interfaces

Method to start Ubuntu 15.04 with systemd

Refer https://wiki.ubuntu.com/systemd

Change boot loader configuration

Boot loader configuration

After installation, the machine will still boot under upstart by default. To boot under systemd, the following argument must be specified on the kernel command line:

Note that the systemd binary resides now in /lib/systemd/ and /bin/systemd is just a symlink to it.

To boot under systemd by default, edit /etc/default/grub and change the following line:

After modifying any grub related configuration files like /etc/default/grub the following command is needed to bring the changes into effect.

After above step, reboot the machine. Post reboot, verify that systemd is running using 'ps ax| grep systemd' command

Method to upgrade Ubuntu 14.04 to ubuntu 16.04

Refer https://wiki.ubuntu.com/XenialXerus/ReleaseNotes

Steps to upgrade ubuntu 14.04 to ubuntu 16.04

o upgrade on a server system:

• • Install the update-manager-core package if it is not already installed.

  • Make sure the /etc/update-manager/release-upgrades is set to normal if you are using 15.10, lts if you are using 14.04 LTS.

  • Launch the upgrade tool with the command sudo do-release-upgrade.

  • Follow the on-screen instructions.

How to change hostname of machine without restart

change hostname without restart using hostnamectl

root@ubuntu:~# hostnamectl set-hostname master

root@ubuntu:~# cat /etc/hostname

master

root@ubuntu:~# hostnamectl set-hostname master1

root@ubuntu:~# cat /etc/hostname

master1

root@ubuntu:~# exit

logout

Connection to 10.102.53.236 closed.

Deepaks-MacBook-Air:~ deepak$ ssh root@10.102.53.236

root@10.102.53.236's password:

Welcome to Ubuntu 16.04 LTS (GNU/Linux 4.4.0-21-generic x86_64)

* Documentation: https://help.ubuntu.com/

212 packages can be updated.

114 updates are security updates.

Last login: Thu Nov 30 23:44:14 2017 from 10.150.16.22

root@master1:~#

Reference: https://askubuntu.com/questions/87665/how-do-i-change-the-hostname-without-a-restart

Method to install KDE in ubuntu

use apt install kubuntu-desktop

In case, you face error, Refer https://askubuntu.com/questions/764542/help-installing-kubuntu-desktop-on-ubuntu-16-04

Method to turn off swap memory permanently

swaoff -a will turn off swap area for a same session and will vanish on reboot

change /etc/fstab to disable swap memory command for disabling swap across reboots

Disable swap across reboots

root@master1:~# cat /etc/fstab

# /etc/fstab: static file system information.

#

# Use 'blkid' to print the universally unique identifier for a

# device; this may be used with UUID= as a more robust way to name devices

# that works even if disks are added and removed. See fstab(5).

#

# <file system> <mount point> <type> <options> <dump> <pass>

/dev/mapper/ubuntu--vg-root / ext4 errors=remount-ro 0 1

# /boot was on /dev/xvda1 during installation

UUID=d337042b-0d54-4a25-b46c-366ee4b44f0a /boot ext2 defaults 0 2

#/dev/mapper/ubuntu--vg-swap_1 none swap sw 0 0

root@master1:~#

Useful link: https://askubuntu.com/questions/440326/how-can-i-turn-off-swap-permanently

Method to ensure trust while downloading package from a new site

use apt-key

Establishing trust with docker site using apt-key

deepak@deepak-VirtualBox:~$ sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

OK

deepak@deepak-VirtualBox:~$ sudo apt-key fingerprint 0EBFCD88

pub 4096R/0EBFCD88 2017-02-22

Key fingerprint = 9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88

uid Docker Release (CE deb) <docker@docker.com>

sub 4096R/F273FCD8 2017-02-22

deepak@deepak-VirtualBox:~/personal/docker$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg

-----BEGIN PGP PUBLIC KEY BLOCK-----

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YT90qFF93M3v01BbxP+EIY2/9tiIPbrd

=0YYh

-----END PGP PUBLIC KEY BLOCK-----

deepak@deepak-VirtualBox:~/personal/docker$ ^C

Useful link: man page of apt-key

https://docs.docker.com/engine/installation/linux/docker-ce/ubuntu/#set-up-the-repository

Method to resolve apt-get update error

Refer https://www.youtube.com/watch?v=1zKJRRtEZ40

Understand buff/cache entry in the free command output

Interpretation of free tool output

nterpretting output of free:

The first line of the free output lists:

• • total Your total, physical (assuming no virtualization) memory

  • used How much of that is currently used (by anything)

  • free How much of that is completely free (not used at all)

  • shared (never anything there, ignore that column)

  • buffers Memory used by kernel buffers

  • cached Memory used for cache

The last two items, cache and buffers, is memory that is not allocated to specific user processes. It is memory reserved by the kernel to improve performance overall, but is not "application" memory. These areas will grow or shrink depending on kernel policies with respect to caching, memory pressure, application I/O patterns, etc.

Useful link: https://askubuntu.com/questions/223759/how-to-interpret-output-of-free-m-command

Method to copy only directories

Use below command

find -type d -links 2 -exec mkdir -p "/path/to/backup/{}" \;

Refer https://askubuntu.com/questions/365877/copy-only-folders-not-files

Cleanup /boot space

Use https://help.ubuntu.com/community/RemoveOldKernels

Reference: https://unix.stackexchange.com/questions/450914/errors-were-encountered-while-processing-var-cache-apt-archives-linux-image

Reference

init=/lib/systemd/systemd

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash init=/lib/systemd/systemd"

update-grub