Linux: Difference between revisions

Revision as of 07:59, 10 October 2012

Commands

System

Syntax	Action / Description
`shutdown -r now`	Restart / reboot system, use `-h` to shutdown/halt. If command not available use `init`
`init <level>`	Level 0 - Halt system, level 6 - Reboot system
`uname -a`	Running OS info
`arp -n`	IP -> MAC arp table
`ifconfig`	Interface config (Unix equiv of Windows' ipconfig)
`ps fx \| grep <proc>`	Find running process info
`ps -aux`	Running process info
`kill <pid>`	Kill a process
`top`	Task Manager (ish)
`free -m`	Free memory
`nice <cmd>`	Runs a command with reduced priority

File System and File Operations

Syntax	Action / Description
`ls -l`	List directory contents (`-l` long format) - see [[#Terminal Colours\|Terminal Colours]
`df -h`	Disk space summary
`df -i`	Disk inodes summary
`du -sh`	Directory space usage summary
`du -ma / \| sort -nr \| head -n 20`	Find 20 largest files/directories
`pwd`	Present working directory
`cp <src> <dest>`	Copy a file (see also `scp`)
`ln -s <src> <dest>`	Create a symbolic link to a file
`rm –i <file>`	Remove (delete) file (`-i` prompts before remove)
`rm –d -r -f <folder>`	Remove (delete) folder and contents without prompting
`find /path/ -iname "FILENAME"`	Find file with filename in path
`find <folder> -mtime +14 -exec rm {} \;`	Remove (delete) files in folder older than 14 days
`chmod +x <file>`	Add execute permission to a file
`lsof <folder>`	List open files
`tar czf file.tgz folder`	Tar contents of folder to file

File Contents (Inspection and Manipulation)

Syntax	Action / Description
`more <file>`	Views a file (read only), `q` to exit, `+line` to start from line
`less <file>`	Views a file (read only), like `more` , but with increased functionality
`watch -d "ls -lt *.vmdk ;date"`	Watch modifications occurring to files matching *.vmdk
`diff <file1> <file2>`	Difference between two files
`grep <find> <file>`	Find all occurrences of find in file
`tail <file>`	Displays the last 10 lines of a file, `-f` follows any updates (eg to monitor a log file)

NTP / Date and Time

Syntax	Action / Description
`date`	Show the local system date and time
`date -d <string>`	Show/calculate the date and time represented by `<string>` (eg 'tomorrow', 'next week', 'thursday')
`ntpdate -p 1 -q -d ntp.domain.com`	Test/query an NTP server (replace `ntp.domain.com`)
`ntpdate -d ntp.domain.com`	Set system clock from an NTP server (replace `ntp.domain.com`)
`ntpq -p`	Show list of ntp daemon peers

System Info

File	Description
`/proc/cpuinfo`	CPU(s) information - model, spec, features, etc

Terminal Colours

The colourisation of files and folders as seen through a terminal session (eg PuTTY) normally have the following meanings...

Type	Description
FILE	Normal file
MISSING	Missing file
DIR	Directory
EXEC	Executable file
LINK	Symbolic link
ORPHAN	Orphaned symbolic link
FIFO	Named pipe
SOCK	Socket
BLK	Block device driver
CHR	Character device driver
ARC	Archive / Compressed
MEDIA	Media files (image, video etc)

These colours are derived from the ISO 6429 standard for coded character sets. The above info is derived from the following sources...

SCP

In order to be able to copy files from one machine to the other...

scp user@server:/remote/server/path/file /local/server/path/

In order to be able to copy files within a script (and not get prompted for a user password, the public key of the machine running the script needs to be authorised on the remote server.

On the local machine, be logged in as the same user as will be running the script
Create public key on local machine (just hit return to accept default options)
- ssh-keygen -t rsa
Copy the public key for local machine user to the remote machine
- EG scp /root/.ssh/id_rsa.pub server:/home/user/
On the remote machine, check if the following file already exists
- /root/.ssh/authorized_keys
If so, append the contents of the copied key to the file
If not, copy the file

VI Editor

VI is a bit of a pain to use, go slowly, and use [Esc] regularly to get out of the current mode after each operation.

Crib sheet for VI mode commands...

Command	Purpose
`i`	Insert characters
`x`	Delete character
`r`	Replace character
`cw`	Overwrite word (use any delimiter)
`o`	Insert line
`dd`	Delete current line
`<x>yy`	Yank (copy) next x lines (inclusive of current line, default `x` is 1)
`p`	Paste yanked lines
`/<string>`	Search for next occurrence of string
`:g/<find>/s//<replace>/g`	Find and replace
`:wq`	Write (save) and Quit
`:q!`	Quit (don't save)
`:undo`	Undo last action

Unix User accounts

Create Account - Use useradd <user> to add a new user account with the default policy settings
Modify Password - Use passwd <user> to change password for user. To breach minimum complexity rules you must be logged in at the console (in the DC not remotely)
Modify Expiry - To disable the password expiry policy for a account that already exists use chage -M 99999 <user> , to disable for all future account (ie modify the default policy) use esxcfg-auth --passmaxdays=99999

@@ Line 94: / Line 94: @@
 |-
 |<code> ntpdate -d ntp.domain.com </code> || Set system clock from an NTP server (replace <code>ntp.domain.com</code>)
+|-
+|<code> ntpq -p </code>                   || Show list of ntp daemon peers
 |}