Linux

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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
df -h Disk space summary
df -i Disk inodes summary
du -sh Directory space usage summary
du -h --max-depth=1 Directory space usage summary of subfolders
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
find -iname 'file*' -mtime +7 -exec rm {} \; Remove all files matching file* in current folder older than 7 days
find -iname 'file*' -exec rm {} \; -exec sleep 1 \; Remove all files matching file* in current folder, pausing for 1 sec between deletes
chmod +x <file> Add execute permission to a file
lsof <folder> List open files
lsof +L1 List deleted files still held open (reported by df but not du
tar czf file.tgz folder Tar contents of folder (or file) to an archive
mount --bind /var/tmp tmp Create a /tmp mount to local /var/tmp directory

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> Show all lines with occurrences of find in file
grep -A <n> -B <m> <find> <file> As above, but additionally show the n lines after and m lines before
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 / Command Description
/etc/issue OS Name
/proc/cpuinfo CPU(s) information - model, spec, features, etc
egrep -i 'network|ethernet' List NICs

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.

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

Alternatively...

  1. On the local machine, be logged in as the same user as will be running the script
  2. Create public key on local machine (just hit return to accept default options)
    • ssh-keygen -t rsa
  3. Copy key to remote machine
    • cat /root/.ssh/id_rsa.pub | ssh user@server "cat >> ~/.ssh/authorized_keys"

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
  • List users - cat /etc/passwd
  • List groups - cat /etc/group
  • Show group membership - id <user>
  • Add user to group - usermod -a -G <group> <user> - user must already exist