System administration: Difference between revisions

== Set timezone ==

$ sudo timedatectl set-timezone America/Denver

== Composer ==

Composer is a PHP package management tool.  Usually needed for setting up web application development environment.

$ cd

$ mkdir bin

$ ./getcomposer

$ mv composer.phar composer

Create private/public SSH key file using the default bit encryption and with a comment. The command creates files under ~/.ssh folder.

$ ssh-keygen -C user@host.domain

The config file ~/.ssh/config stores information about various SSH connections, and allows the definition of hostname, username, ports, and other settings.

Host hostname1

     HostName hostname1.domain.com

     User username1

     Port 1234

== Adding a user to sudoers list ==

On Ubuntu distribution of GNU/Linux, you can uncomment force_color_prompt = yes line to use color prompts. The following is my personal favorite color configuration for the prompt.

PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u\[\033[01;30m\]@\[\033[00;36m\]\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

== Enable byobu ==

$ byobu-enable

== Update .vimrc ==

syntax on

set noexpandtab

autocmd FileType php nnoremap <C-p> :call PhpDocSingle()<CR>

autocmd FileType php vnoremap <C-p> :call PhpDocRange()<CR>

=== awesome-vim ===

$ git clone --depth=1 https://github.com/amix/vimrc.git ~/.vim_runtime

$ sh ~/.vim_runtime/install_awesome_vimrc.sh

<nowiki>#</nowiki> makes this unecessary, but i'm not that good yet.)

Install the LAMP stack

$ sudo apt-get install tasksel

$ sudo tasksel install lamp-server

Install git and other PHP related extensions

$ sudo apt-get install git php5-mcrypt php5-xdebug php5-intl

=== .gitconfig ===

[core]

   editor = vim

[merge]

   defaultToUpstream = true

== Change default shell ==

$ chsh

== Edit passwd files ==

$ sudo vipw

= RHEL-specific =

== Update the server ==

$ sudo apt update && sudo apt -y full-upgrade && sudo apt-get -y autoremove

== Reconfigure console font ==

$ dpkg-reconfigure console-setup

== Change the default editor ==

Used by visudo and other programs for invoking an editor.

$ sudo update-alternatives --config editor

== Change time zone ==

* First determine your own shell

$ tty

* Show all of your running processes

$ ps -fu mhan

UID        PID  PPID  C STIME TTY          TIME CMD

mhan    21939 21609  0 19:06 pts/3    00:00:00 ps -fu mhan

mhan    21580 21469  0 19:02 ?        00:00:00 sshd: mhan@pts/2

* If I want to kill pts/2 then the PID to kill is 21580.

$ kill -HUP 21580

Reference: https://kb.iu.edu/d/adqw (accessed on 10/5/2017)

As an example, let's say the process of interest is ''qemu-system-arm''. You have to find out what PID (Process ID) is first.

$ pidof qemu-system-arm

3016

Then check what the current nice value of the process is:

$ ps -o pid,comm,nice -p 3016

   PID COMMAND        NI

  3016 qemu-system-arm  0

According to the output, the nice value of ''qemu-system-arm'' is 0. We want to '''decrease''' the nice value to dedicate more CPU time to it. However, you need sudo privilege in order to give a negative value for a nice value, even though you do not need such privilege for increasing the nice value to something above 0. Here we decrease it to -10.

$ sudo renice -10 -p 3016

To set a permanent priority on all processes for a specific user or a group you can update ''/etc/security/limits.conf'' file.

== Pull a random line from a log ==

$ shuf -n 1 /etc/pihole/gravity.list

== Viewing of the log in real time ==

$ tail -f /var/log/some.log

[[Multitail]]

== Remove some columns from an output ==

$ ls -l | awk '{print $3 " " $9}'

== Make a backup without typing the full path twice ==

To make a backup without typing the full path twice with the suffix .orig

$ cp /long/path/to/file/name{,.orig}