TOC:
- [Basic commands] (#Basic-commands)
- Users
- Files
- Bash
- Networking
- System
- List of commands
- Make a bootable drive
- Mount a shared drive
- ls
- cd
- pwd
- mkdir
- cp
- rm
- find
- cat
- grep
- which
- echo
- cut
- sort
- type
- stat
- tee
- chmod
- umask
- setfacl
- getfacl
- uname
- id
- who
- ps
- top
- kill
cd : Change dir
cd directory
-> moves to specified directory
cd
-> returns to 'home dir' eg: for user 'penguin' = /home/penguin
cd ..
-> moves one dir UP
cd -
-> returns to previous working directory
pwd : Print (actual)working dir = 'where am I now ?'
pwd
/home/penguin
mkdir : Make dir
mkdir -p /home/penguin/AWS/BigData/Mobile
-> -p = make all 'parent dirs if they do not exist !
find
find . -type f -name 'test*' -> return all files under this dir starting with 'test'
find . -type f -iname 'test*' -> idem but 'i' makes it CASE INSENSITIVE !!
find . -type f -name '*.json' -maxdepth 1 -> search only 1 dir deep = 'this dir'
find . -type f -name '*json' -maxdepth 1 -exec rm {} +
-> executes 'rm' on all found files in THIS dir (+=end)
find . -type f mmin -10 -> find changed files < 10 minutes in this dir.
find . -type f mmin +5 mmin -15 -> returns chenged file between 5 and 15 min
find . -type f mtime -10 -> returns files changed within last 10 days
find . -type f ctime
find / -name "*.json" -print 2>/dev/null -> find under root('/'), all 'json-files' and blackhole errors (2=stderr) (cfr permission denied)
find / -user penguin -name "Book*" -print 2>/dev/null
find / -size +5M -> find files > 5M in root dir (use k=KiloByte and G=Giga)
find / -empty -> find all O byte files
find / -perm 777
find myWebsite -exec chown penguin:www-data {} +
-> -exec .. to execute a cmd
-> user=penguin group=www-data
-> {} placholder for find result and + ='end of exec'
find myWebsite -type d -exec chmod 775 {} +
-> sets all dir+subdir permissions to 775
find myWebsite -type f -exec chmod 644 {} +
-> sets all file permissions to 644
!Check it!
find myWebsite -chmod 775
ind myWebsite -chmod 664
grep Global Regular Expression Print
umask
Dicates the default file permission set.
How ?
- umask = 0022 (default)
- permissions = 0666 -umask = 0644 (rx-|r--|r--)
ps bin: directory boot: directory cdrom: directory dev: directory etc: directory home: directory lib: directory lib64: directory lost+found: directory media: directory mnt: directory opt: directory proc: directory root: directory run: directory sbin: directory snap: directory srv: directory sys: directory tmp: sticky, directory usr: directory var: directory ps (with no '-') = BSD syntax ps - = Unix/Linux syntax
Mixing both, BSD and Unix/Linux, can become confusing!
remark = both are different !!! eg 'ps aux >< ps -aux'
ps -> shows running **processes** in current shell' (default ps is filtered!)
ps -f -> show 'full' (details) -including 'Parent PIP = PPID'
ps -l -> show 'long' (details) -> even more then '-f'
ps -e == ps -A -> shows 'all' processes or deamon = process with no relation to tty
ps -a -> shows 'all' processes - -related with tty terminal
ps -u -> add 'user info'
ps -aux -> show 'all' (-a) processes for 'user'(-u) and 'user=x(all users)'
ps -aupenguin -> show 'all' (-a) processes for 'user'(-u) and 'user=penguin'
ps x -> !BSD notation! = lift the tty restriction
ps a -> !BSD notation! = lift the 'only yourself restriction
ps u -> !BSD notation! = full details (u user oriented format)
ps aux -> !BSD notation! = all processes
ps ax == ps -ef -> (a all process) == (-e every process long_format)
top
Shows top processes
top
kill
kill 1297 -> kills process PID=1297
- file location = /etc/passwd
- stored in ETSI format = 7 fields
example:
useradd penguin -m -s /bin/bash -g users
-> -m = create home dir for this user (/home/penguin)
-> -s = default bash for this user
-> -g = belongs to group
How to delete a user?
userdel -rf polarbear -> -r deletes /home/polarbear dir + mail -f = force (even if logged in)
Remark: you have to have permission in order to create users , usually 'root'.
groupadd -g 916 testers -> adds a group (see /etc/group) with id=916 named 'testers'
How to make a user be member of multiple groups? -> edit /etc/group and add all groups (separated with ',')
penguin:x:1000:users,testers -> user 'penguin' now member of 'users' and 'testers
Remark: You have to : 'apt-get install sudo' (sometimes sudo is not installed-> no '/etc/sudoers' file)
If everybody can login as root -> BAD. Because in case of problem there is no way of actually knowing who did it. Solution = give specific users 'root rights' and then they can perform 'sudo ...' under there login account.
cat /etc/group -> lists all the (user)groups
cat /etc/sudoers -> add user to
passwd penguin -> as 'root' we can set anybody's password!
Config: /etc/sudoers
How to add a user to 'sudo' ?
-
login as 'root'
-
Create user: 'useradd penguin -m -s /bin/bash -g users'
-
Create passwd: 'passwd penguin'
-
Add user to sudoers: 'usermod -aG sudo penguin'
-
test:
- 'su penguin'
- 'sudo ls /root' -> if access then ok :-)
Everything is a file in linux !
- '/' = root dir
- '/root' = home dir for root user -> ! not in /home
- '/bin' = dir for programs
- '/boot' = files required for starting your system -> 'DO NOT TOUCH !!'
/boot/grub/grub.conf or menu.lst: boot loader
/boot/vmlinuz: Linux kernel
- '/dev' = contains device files
- null = 'black hole' eg:as stdout for files - /dev/null
- tty = 'teletype' = your terminal window
- ttyS0 = serial port (physical device)
- pts = 'pseudo terminal slave' = remote connections eg SSH (no physical device)
**remark**
- c = 'Character device' -> eg see tty
- b = 'block device' = acts as a disk
- '/etc' = Everything To Configure -> contains mainly configuration files (eg passwd file, ...)
contains also a collection of scripts to start system services at boot time
Everything is readable text
Interesting files
- /etc/crontab: automated jobs
- /etc/fstab: a table of storage devices and their mount points
- /etc/passwd: user accounts
- '/home' = dir for working dir for users. eg: /home/penguin or /home/user2
- '/lib' = shared libraries (conf. dll in Windows)
- '/lib64' = 64 - bit libraries
- '/media' = external plugable media (mainly storage) eg USB drives
- '/mnt' = mount = for manualy mounting drives. Today not used very much (? except Docker ?)
- '/opt' = for installation of add-on software. Mainly used for commercial software products.
read-only and self-contained software. That is, software that does not split their files over bin, lib,
share, include like well-behaved software should.
<strong>remark: <\strong> there is a subtile difference between /opt and /usr/local
- '/proc' = virtual filesystem maintained by the kernel. The files in this directories are peepholes into the
kernel. The files are readable and will give you a picture of how the kernel sees the computer
created every launch- with info about your computer: CPU, kernel, etc
- '/root' = home directory for root user
- '/run' = (new dir) where system processes write temp data -> DO NOT TOUCH !!
- '/sbin' = dir for 'superuser' programs (eg fdisk)
- '/tmp' = temporary files
- '/usr' = all system-wide, read-only files installed by (or provided by) the OS
- '/usr/bin'= executables installed by the Linux distribution. Holds a great number of programs
- '/usr/lib'= shared libraries for the programs in /usr/bin
- '/usr/local'= system-wide, read-only files installed by the local administrator (usually, you). And that's why most
directory names from /usr are duplicated here.
- '/usr/sbin' = system adm programs
- '/usr/share'= shared data for programs in /usr/bin. eg. conf files, icons, screen backgrounds, sound files
- '/usr/share/doc' = documentation for programs in /usr/share
- '~/.local'= the per-user counterpart of /usr/local, that is: software installed by (and for) each user. Like /usr, it
has its own ~/.local/share, ~/.local/bin, ~/.local/lib.
- '~/.local/opt'= the per-user counterpart of /opt
bin: directory boot: directory cdrom: directory dev: directory etc: directory home: directory lib: directory lib64: directory lost+found: directory media: directory mnt: directory opt: directory proc: directory root: directory run: directory sbin: directory snap: directory srv: directory sys: directory tmp: sticky, directory usr: directory var: directoryy days'. Now mish-mash of directory with: apps,libs,docs,wallpaper,icons, etc - '/srv' = dir for servers. eg: /srv/www (with html for your site) or /srv/ftp - '/sys' = virtual dir - contains info about connected devices -> DO NOT TOUCH !! - '/tmp' = tempory dir mainly used by runnings applications - '/var' = mainly used for log files
**Remark : ** - '~' = short for home dir, for user 'penguin' this is: /home/penguin
- first char = file type
- permission Classes (user, group, Other users)
- read / write / execute (r/w/x)
- ther is a subtile difference between 'Other' and 'All -> see Chmod 3.4
```
| r w x | r w x | r w x
file type | user | group | Other
x | x x x | x x x | x x x
```
example:
| r w x | r w x | r w x
file type | user | group | Other
- | 1 1 0 | 1 0 0 | 1 0 0
- | 6 | 4 | 4 == chmod 644 == user can read/write and rest can read
remark: | 1 1 1 | == 7 => chmod 777 set read/write/execute for user/group/all = max privilage
Also called: symbolic notation versus numeric notation
first char
* - : regular file
* d : directory
* l : symbilic link
* c : device file of type character (see /dev/tty)
* b : device file of type block (see /dev/sd)
* s : socket
* p : pipe
* D : Door (only on Solaris)
2 types:
- 'ln' hardlinks -> They share Inode number (? disk-file partition)
- 'ln -s' symbolic links -> They ** DO NOT** share Inode numbers (have different Inode nr)
Remarks :
Sharing or not sharing same Inode has major consequences: rem: 'ls -i' gives Inode number
HardLinks
- links are 'pointers' to the same Inode
- file type = '-'
- Thus if file to which the link refered is deleted -> link stays intact because Inode nr stiil exists
- if Chmod on file -> this is on Inode -> thus for ALL links
Symbolic Links
- links point to different Inode
- file type = 'l' = link
- it only references the absolute path name
- Thus if file to which the link refered is deleted -> = destroyed -> abs path point to nothing
- permission of link is always 777 -> Permission of 'destination file' determines what can!!
Intro: Difference for files and directories !
-> for files r w x = evident
-> for dir:
- r = you can ls dir
- w = you can 'cp' files into dir
- x = you can 'cd' into dir
Remark: You can not have execute -x permission without read -r permission
See 'man chmod'
Format symbolic mode:
- ugoa
- u = user
- g = group
- o = other
- a = all = u+G+o !!! (see remark 3.2 subtile difference)
chmod u=rwx myfile.txt -> sets rwx to user
chmod u-x myfile.txt -> prohibits x (execution) for user
chmod u+x myScript -> adds x permission tot user
Format numeric mode:
rwx = _ _ _ in binary
eg:
- 000 == ---|---|---
- 400 == 100|000|000 == r--|---|---
- 644 == 110|100|100 == rw-|r--|r--
- 775 == 111|111|101 == rwx|rwx|r-x
- 777 == 111|111|111 == rwx|rwx|rwx
chmod 644 myfile.txt -> sets rw-|r--|r--
chmod 777 myfile.txt -> sets rwx|rwx|rwx
First line specifies permissions of the actual dir (see 'dot' at the end)
chmod 755 . -> sets the permissions as above on the actual directory
Remark: if cmd not found -> run 'apt-get install acl'
ACL = Access List
-> if applied we see a '.' at the end of the permissions
-> enables us to give specific permissions to users
getfacl
setfacl
Now we see a '+' at the end of the permissions indicating one or more additional 'acl'
Bash = Born Again Shell
- Standard Input - default = keyboard
- Standard Output - default = display
- Standard Error - default = display
- '*' = match anything zero or more
- '?' = match anything but only one char
- '[a-z]' = match a lowercase char between a and z
- '!' = for running a cmd nr
- ';' = for separating and executing multiple commands
ls Pete* -> will match 'Pete', 'Peter', Petersen', etc
ls Pete? -> will match 'Peter' but not rest from above
ls Pete?* -> will match everything from above except 'Pete'
ls Pete[r,rsen] -> will match 'Peter' and 'Petersen'
!41 -> This runs the 41-th cmd from your 'history' eg: history
cat /etc/passw | grep penguin ; su penguin ; cd /home/penguin/data -> eg ; = multiple cmds
Remark: All variables exits only in the shel and not the child shells (cfr bash in bash) unless you EXPORT them !!!
PS1='\u@\h$ ' -> defines the prompt variable with 'user@host$'
myCar = 'Mustang'
- < = redirect input
- > = redirect output
* '> file' -> redirects stdout to file
* '1> file' -> redirects stdout to file
* '2> file' -> redirects stderr to file
* '&> file' -> redirects stdout and stderr to file
grep penguin < /etc/passwd -> take '/etc/passwd' as input for grep
cat /etc/passwd | grep penguin > mylog.txt -> output of 'cat+grep' is redirected to file. Thus not visible on screen.
- ~/.profile -> for environment variables (cfr $PATH) + NON specific bash config (must support bash/Zsh/..etc)
- ~/.bashrc -> for interactive bash settings: bash aliases, bash prompt, favorite editor etc
- ~/.bash_profile -> loading ~/.profile + ~/.bashrc (rem ubuntu has no .bash_profile but .profile)
example '~/.bash_profile'
. ~/.profile<br>
. ~/.bashrc
Sourcing a file means 'reading' the file and 'executing' every line in this file as if it was typed at the prompt. If we edit '.bash_profile' we have to 'run' this file to take effect.
source .bash_profile <br>
. .bash_profile = same as above (cfr 'type .' )
Ther are 4 prompts
- PS1 = primary (normal) prompt
- PS2 = when entering a incomplete command -> default = '>' = means enter more stuff
- PS3 = when using a 'select' statement - when scripting
- PS4 = when debugging
PS1 and PS2 are mostly used.
While 'true' + enter -> prompt becomes 'PS2'. Then we enter some commands and after executing we return to PS1. Result: do 'ls' and after 10 sec clear screen.
\$ while true
> do ls -al sleep 10 clear done
Remark: Set PS2 = "Did you forget something? #" -> this way it will be ealisy noticed if you mistyped something! Don't foreget to EXPORT is in .bashrc
alias -> lists all aliases alias l='ls -laih' -> l=long a=all i=Inode nr h=human readable size (K/M/G) <br>
alias mydate='date +"%d:%m:%Y"' -> output = '13:04:2019'
This is the next thing after 'aliases'. Ideal for executing multiple commands at once. Function are run in memory and are therfore faster than scripts or aliases
You can add them in '.bashrc' and call them in the shell. eg: 'myRef'
function myRef () { source ~/.profile source ~/.bashrc clear date }
Both are used to config various parameters of the shell.
set -o -> lists all set parameters
set -o noclobber -> 'to clobber = overwrite unintentionally ! '-o turns it ON'= you can NOT overwrite (default) set +o noclober -> '+o turns it FF' -> you can overwrite a file
shopt -> list all shopt parameters shopt -s cdspell -> tries to correct and match existing cmd
shopt login_shell -> if it returns Off then => 'non login shell' (cfr bash in Docker or Mac)
-> if Onn => login shell (cfr SSH)
Remark: Difference is that with 'login shell'- reads .bash_profile AND .bashrc With 'non login shell' - it ONLY sources (reads) '.bashrc' !!!
Remark: you may need to install some libraries if 'cmd not found
apt-get update
apt-get install iputils-ping -> needed for ping
apt-get install dnsutils -> needed for dig
- ping
- traceroute
- ftp
- scp
- ssh
- dig
- host
- whois
- telnet
- ifconfig
- /etc/hosts
- /etc/nsswitch.conf
- /etc/sysconfig/network-scripts
- /etc/resolv.conf
ping
ping -c 5 google.com
ipv6
ping6 -v -I ip6tn10 2a00:1450:400e:80d::200e
-> -v = verbose -I= interface out (ip6tn10)
-> tip: make alias: 'alias p6='ping6 -v -I ip6tn10'
p6 2a00:1450:400e:80d::200e -> used with the alias
Remark : Define your ip addresses + hostname in 'hosts' to make yor life easier eg: 192.168.2.234 fw -> 'ping fw'
traceroute
traceroute google.com
dig
A tool to troubleshoot and solve DNS problems
dig wizzkid.com -> queries the (default) DNS server and returns (default) 'A record'
dig @8.8.8.8 wizzkid.be -> idem but now we specify a (other) DNS server
dig wizzkid.be MX -> idem but returns MX (mail) record
dig wizzkid.be NS -> returns 'Authoritative' Name Servers (holds the records)
dig wizzkid.be TXT
host
host -> list all host options
host -v google.com -> verbose - detail info: A, AAAA, MX, etc records
ifconfig
ifconfig -a -> all ip/ipv6 - MAC info
- /etc/hosts -> for configuring hostnames & Ip addresses
- /etc/nsswitch.conf -> dictates where to look first: locally/server x,.. ! cfr DNS, passwords,..
- /etc/resolv.conf -> resolve restrictions eg: max 3 DNS entries
Start sequence:
- Bios
- master bootloader (=part of the disk)
- kernel
TCP Wrappers
- /etc/hosts.allow
- /etc/hosts.deny
In both files yo can specifiy what TCP connection can be allowed
| command | description |
|---|---|
| ls -a | list all files including hidden file starting with '.' |
| ls --color | colored list [=always/never/auto] |
| ls -d | list directories - with ' */' |
| ls -F | add one char of */=>@ |
| ls -i | list file's inode index number |
| ls -l | list with long format - show permissions |
| ls -la | list long format including hidden files |
| ls -lh | list long format with readable file size |
| ls -ls | list with long format with file size |
| ls -r | list in reverse order |
| ls -R | list recursively directory tree |
| ls -s | list file size |
| ls -S | sort by file size |
| ls -t | sort by time & date |
| ls -X | sort by extension name |
| file filename | determine the type of a file |
| file -s specialfilename | used for special files such as /dev/sda, ... |
| file -z compressedfile | used for compressed files |
| less filename | read contents of text file one page(one screen) per time |
| less -N filename | shows linenumbers |
| less navigationkeys | navigation |
| /characters | forward search for a pattern which will take you to the next occurrence. |
| n | for next match in forward |
| N | for previous match in backward |
| ? | search for a pattern which will take you to the previous occurrence. |
| n | for next match in backward direction |
| N | for previous match in forward direction |
| CTRL+F | forward one window |
| CTRL+B | backward one window |
| CTRL+D | forward half window |
| CTRL+U | backward half window |
| j | navigate forward by one line |
| k | navigate backward by one line |
| G | go to the end of file |
| g | go to the start of file |
| q or ZZ | exit the less pager |
| 10j | 10 lines forward. |
| 10k | 10 lines backward. |
| CTRL+G | show the current file name along with line, byte and percentage statistics. |
| v | using the configured editor edit the current file. |
| h | summary of less commands |
| &pattern | display only the matching lines, not all. |
| ma | mark the current position with the letter ‘a’, |
| 'a | go to the marked position ‘a’. |
| zless filename | version of less for compressed files (.gz) |
| mv src dst | move/rename file src to dst |
| cp src dst | copy src to dst |
| rm src | delete src |
| mv/cp/rm -v | verbose option, shows what is done |
| mv/cp/rm -i | interactive option, asks for confirmation |
| type cmd | command's type: executable, shell built-in, shell function, alias |
| which executable | show executable's location |
| help cmd | get help for shell built-in command |
| cmd --help | usage information on command |
| man cmd | display manual page |
| apropos searchterm | shows list of manpages related to searchterm |
| whatis cmd | brief description of command |
| info cmd | GNU only, alternative to man pages |
- Insert your USB drive
- open the “Disks” utility
- Choose your USB drive from the available drives on the left
- First we need to delete the old partitions that remain on the USB key.
Open a terminal and type sudo su
Type fdisk -l and note your USB drive letter.
Type fdisk /dev/sdx (replacing x with your drive letter)
Type d to proceed to delete a partition
Type 1 to select the 1st partition and press enter
Type d to proceed to delete another partition (fdisk should automatically select the second partition)
- Create new partition(s)
Type n to make a new partition
Type p to make this partition primary and press enter
Type 1 to make this the first partition and then press enter
Press enter to accept the default first cylinder
Press enter again to accept the default last cylinder
Type w to write the new partition information to the USB key
Type umount /dev/sdx (replacing x with your drive letter)
Type mkfs.vfat -F 32 /dev/sdx1 (replacing x with your USB key drive letter)
REMARK: the last two steps can be done from the Disks utility
- open the “Disks” utility
- Choose your USB drive from the available drives on the left then click the stop button to unmount the drive
- Click the “gear” icon and then click Format Partition
- Give the volume a name. Use underscore or hyphen iso spaces. Choose option FAT
- When the format is complete you can click the “Play” button to mount the drive
- Before we copy the files to our USB stick using 7-zip (‘7z x’ command), let’s display our USB drive info and Downloads folder listing so we have an easy reference
$ df -h | grep -i media
$ ls ~/Downloads
$ 7z x ~/Downloads/ubuntu-18.04.1-desktop-amd64.iso -o/media/blah/Ubuntu_UEFI/
- Check to see if the USB drive now contains files with the ‘ls’ command
Shared drive on server NAS/path will be mounted on /mnt/backup/
sudo mount -v -t cifs //NAS/path/ /mnt/backup/ -o username=username (on server) ,password=password (on server)
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