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Basics stuff one looks up all the time

Moving around system

cd path/to/dir to change directory, cd .. to move one dir up

pwd to write out current absolute path e.g. /home/user/.ssh

ls to write out the content of current dir (possible append with path ls some/place), popular options include:

  • -a for all, -A for all without . and ..
  • -l for long format, -g just without author, -G without group
  • -F to append one of */=>@|) to entries
  • --color=always to show colours
  • -h for man-readable, useful with -l and -s
  • -s print size in blocks
  • -r to reverse order
  • -S sort by size, descending
  • -t sort by time creation, descending
  • -clt sort by ctime (modification), descending
  • -ut sort by access time, descending
  • -U no sorting
  • -X sort by extensions
  • -R for recursive listing
  • -n is like -l but numbers instead of strings

Info and find stuff

uname

to find software info about current OS uname -a

lsb_release

to find info about current release lsb_release -a

neofetch

Install neofetch for pretty print of basic HW and SW info neofetch

which

which command to find the path to command

type

type command to find what kind of command is, whether programme, executable or shell built-in

find

Utilized by find <starting-directory> <options> <search term> and most basic being:

find . -name my-file

Other options are:

  • -iname for case-insensitivity
  • -not for negation
  • -type followed by directory, file, link, character and block device
  • -delete to delete the found files
  • -size <size> <unit>, possible use ckMG for byte, kilo, mega, giga 10M
  • -user by user
  • -group by group
  • -perm by perm (alternative -empty for empty files, -exec for executables and -read for readable)

locate

Alternative to find is locate which indexes your whole system and runs the command on the database. You may install it and run it via following:

sudo apt-get update
sudo apt-get install mlocate
sudo updatedb

File rights + ownership

TODO: write a bit more about these

chmod

chown -Rv user[:group] FILE

chgrg

Multiple TTYs

exit terminal but leaves all processes running

disown -a && exit

Screen

For simple command persistence, use screen, then run your command and leave with CTRL+A D. To come back, use screen -r. If you have more screens running, it'll list all of them with last command and let you choose one of them.

Tmux

it certainly exists.

systemd

Basic command

For system state:

  • systemctl status show current status
  • systemctl --failed show failed units

Checking unit status:

  • systemctl status unit includes whether it's running
  • systemctl is-enabled unit

Management, all requires root/sudo:

  • systemctl start unit
  • systemctl stop unit
  • systemctl restart unit
  • systemctl reload unit (reloads unit's config)
  • systemctl daemon-reload (scan for changes)

Enabling units i.e. starting at boot

  • systemctl enable unit
  • systemctl enable --now unit to enable and start right away
  • systemctl disable unit

adding a service

In etc/systemd/system/your.service we write following

[Unit]
Description=Your service here
After=network.target #what part of system is required
StartLimitIntervalSec=0
[Service]
Type=simple
Restart=always #on-failure option
RestartSec=1 #interval before restarting
User=YourUser #important for file access
ExecStart=/path/to/bin command args

[Install]
WantedBy=multi-user.target

and start it with systemctl start your.service.

Disks and Drives

df -HT,lsblk (no SU), fdisk -l, blkid

Partitions

!BE CAREFUL! Altho fdisk need confirm to write, use print to triple check sudo fdisk /dev/sdx

Filesystems

mkfs.<type> [-j] /dev/sdxn e2label /dev/sdxn "label name"

Mounting

to mount sudo mount /dev/sdxn /where/to

in /etc/fstab add entry and do mount -a

#FS,LABEL= or UUID=  /mnt/pnt/  fstype  options  dump  pass
LABEL=MY_BACKUP    /mount/point  ext4  defaults   1     2

RAM disk

mkdir -p /mnt/ram mount -t tmpfs tmpfs /mnt/ram -o size=8192M

Network stuff

Network Manager CLI

nmcli with one of the following allows you to list, modify, manage connections & device or even allows you to use wifi to scan network, set hotspots or show password

  • g[eneral] NetworkManager's general status and operations
  • n[etworking] overall networking control
  • r[adio] NetworkManager radio switches
  • c[onnection] NetworkManager's connections
  • d[evice] devices managed by NetworkManager
  • a[gent] NetworkManager secret agent or polkit agent
  • m[onitor] monitor NetworkManager changes

E.g. to set wifi to connect automatically, do following:

nmcli connection modify NAME/UUID connection.autoconnect yes

Firewalls

TODO: write a bit more about how to use either of them

All firewall manipulation will require admin privileges.

ufw

IPTables

Printing current rules is done via iptables -L, add -v for more verbosity; iptables -S for exact command wording

To save the rules, use:

sudo apt install iptables-persistent
sudo netfilter-persistent save

Oracle Cloud

If you're setting up service in Oracle Cloud, do not forget to allow particular ports and ips in secure list via webUI. However each Ubuntu and like other image with IPTables need to run following commands to make it work since the defaults make traffic into arbitrary REJECT jump. If you wanna do it right way, add the rules with -I FLOW 5 <rest-of-rule> (or any number before the jump rule specified bellow).

iptables -D INPUT -j REJECT --reject-with icmp-host-prohibited
iptables -D FORWARD -j REJECT --reject-with icmp-host-prohibited

FIXME: wording To add traffic through, modify following; for Oracle Cloud VM Firewall (INPUT on interface ens3, TCP/IP at port 80, state NEW, ESTABLISHED)

iptables -A INPUT -i ens3 (NIC) -p tcp (protocol) --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT

terminal colours

#custom
    PS1='\e[33;1m\u\[\033[00m\]@\[\033[01;32m\]\h\[\033[00m\]: \[\033[01;34m\]\W\e[0m\$ '
#default deb
    PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

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