HowTO Ubuntu System

**ajmorris** · June 27th, 2008

HowTO use and understand your Ubuntu/linux system. NOTE: not all commands are listed obviously, just ones that i thought were important
feel free to message me, or post here, if you think something else should be added. Other comments also welcome.
Ask for support here also if you wish.
Please tell me if it is too difficult to follow -- Note, pressing Ctrl+F in Firefox will allow for searching of key terms

You may also like to see my networking tutorial:
http://ubuntuforums.org/showthread.php?p=5532395

Table of Contents
Finding Some System Info
*Load, statistics and messages
*Running kernel and basic system information
*Information about your hardware
*Kernel Detected Hardware
*Commands for Users and controlling them
*Limits
*Per Shell/Script
*Per User/Process
*System Wide Limits
*Runlevels
*Standard linux runlevels
*Debian Runlevels
*kernel
*Kernel Modules
*Compiling Your Kernel
Listing and manipulating processes
*Listing and Manipulating Processes
*Priorities
*Background/Foreground
*Using Top effectively
*Signals/Kills
File Systems
*Permissions
*Disk Information
*System Mount points
*Disk Usage
*Find out who has which files open
*Find opened files on a mount point with fuser or lsof:
*About and application
*About a Single File
*Mount/remount a file system
*Add Swap on the fly
*Mount a samba share
*Mount an image
*Create and burn an ISO image
*Convert a .nrg file to .iso
*Convert a cue/bin file to .iso
*Create a file based image
*Losetup
*Create a memory filesystem
*Disk Performance

Finding Some System Info

Load, statistics and messages -- useful to find out what is happening in your system

# displays and updates the top cpu processes

Code:

top

# displays your processors related statistics -- install via apt-get install sysstat

Code:

mpstat 1

# displays your virtual memory statistics

Code:

vmstat 2

# display I/O statistics (2 s intervals) -- also installed via sysstat

Code:

iostat 2

# Last 500 kernel/syslog messages

Code:

tail -n 500 /var/log/syslog

# Last 500 kernel/syslog messages

Code:

tail -n 500 /var/log/messages

# System warnings messages see syslog.conf

Code:

tail /var/log/warn

Running kernel and basic system information

# Get the kernel version -- Use uname --help for variations of this command

Code:

uname -a

# Show how long the system has been running and CPU load

Code:

uptime

# system's host name

Code:

hostname

# Display the IP address of the host

Code:

hostname -i

# Description of the file system hierarchy

Code:

man hier

# Show system reboot history

Code:

last reboot

# Full release info of any LSB distribution

Code:

lsb_release -a

# Get Debian version (yes ubuntu gives one, it is based on debian)

Code:

cat /etc/debian_version

Information about your Hardware

Kernel detected hardware

# Detected hardware and boot messages

Code:

dmesg

# information about installed hardware

Code:

lsdev

# Read the BIOS

Code:

dd if=/dev/mem bs=1k skip=768 count=256 2>/dev/null | strings -n 8

# Shows PCI devices

Code:

lspci

# Shows USB devices

Code:

lsusb

# Shows DMI/SMBIOS info (hardware information from the BIOS)

Code:

dmidecode

# Show a list of all devices with their properties

Code:

lshal

# Shows a list of connected hardware

Code:

lshw

# Information about your CPU

Code:

nano -w /proc/cpuinfo

# Info about your hardware memory

Code:

nano -w /proc/meminfo

# Displays your physical memory

Code:

grep MemTotal /proc/meminfo

# Watch changeable interrupts continuously -- Watch -n1 is very useful to watch any changing file

Code:

watch -n1 'nano -w /proc/interrupts'

# Used and free memory (-m for MB)

Code:

free -m

# Configured devices

Code:

nano -w /proc/devices

Commands for Users and Controlling them

# Shows the active user id with login and group

Code:

id

# Shows last logins on the system

Code:

last

# Shows who is logged on the system

Code:

who

# Shows last boot time

Code:

who -b

# Add group "admin"

Code:

groupadd admin

# Adds user Joe Bloggs to group admin

Code:

useradd -c "Joe Bloggs" -g admin -m joe

# Add existing user to group

Code:

usermod -a -G <group> <user>

# Delete user joe

Code:

userdel Joe

To temporarily prevent logins system wide (for all users but root) use nologin.
The message in nologin will be displayed (might not work with ssh pre-shared keys).

# Replace Sorry no login now for the message you would like to display

Code:

echo "Sorry no login now" > /etc/nologin

Limits

Some applications require higher limits on open files and sockets. The default limits are sometimes too low.

Per shell/script

The shell limits are governed by ulimit. The status is checked
with ulimit -a. For example to change the open files limit from
1024 to 10240 do:

Code:

ulimit -n 10240

The ulimit command can be used in a script to change the limits for the script only.

Per user/process

Login users and applications can be configured in /etc/security/limits.conf. For example:

Code:

nano -w /etc/security/limits.conf

# Limit user processes

Code:

*   hard    nproc   250

# Limit application open files

Code:

asterisk hard nofile 409600

System wide limits

Kernel limits are set with sysctl. Permanent limits are set in /etc/sysctl.conf.

# View all system limits

Code:

sysctl -a

# View max open files limit

Code:

sysctl fs.file-max

# Change max open files limit

Code:

sysctl fs.file-max=102400

# port range

Code:

echo "1024 50000" > /proc/sys/net/ipv4/ip_local_port_range

Code:

nano -w /etc/sysctl.conf

# Permanent entry in sysctl.conf

Code:

fs.file-max=10240

# How many file descriptors are in use

Code:

nano -w /proc/sys/fs/file-nr

Runlevels

Once booted, the kernel starts init which then starts rc which starts all scripts belonging to a runlevel.
The scripts are stored in /etc/init.d and are linked into /etc/rc.d/rc#.d with # the runlevel number.

The actual runlevel can be changed with init. For example to go from 3 to 5:

# Enters runlevel 5

Code:

init 5

Runlevel list

* 0 Shutdown and halt

* 1 Single-User mode (also S)

* 2 Multi-user without network

* 3 Multi-user with network

* 5 Multi-user with X

* 6 Reboot

The above is for what most linux OSs do, however, debian acts slightly differently:

* 0 System Halt

* 1 Single User

* 2 Full multi-user mode (Default)

* 3-5 Same as 2

* 6 System Reboot

Debian and systems based on Debain, use the command update-rc.d to manage runlevels scripts.
Default is to start in 2, 3, 4 and 5 and shutdown in 0, 1 and 6.

in the following examples, i will use sshd (the ssh server)

# Activates samba in the default runlevel

Code:

update-rc.d sshd defaults

# For use with explicit arguments

Code:

update-rc.d sshd start 20 2 3 4 5 . stop 20 0 1 6 .

# Disable sshd for all runlevels

Code:

update-rc.d -f sshd remove

# Shuts down and halts the system -- 'now' can be replace with a number # (# minutes from now)

Code:

shutdown -h now

Also, debian tends to want to use a tool called 'telinit' to switch init modes.
i.e. #switches to runlevel 3

Code:

telinit 3

Also, take caution. Whilst you can issue telinit 6 to issue a shutdown... it really is not recommended.

Resetting your root password

EDIT: Has been removed due to this forum policy: http://ubuntuforums.org/showthread.php?t=765414 (thanks Rocket2DMn)

Kernel

Kernel modules

# Lists all modules loaded into the kernel

Code:

lsmod

# To load a module -- I used ndiswrapper here

Code:

modprobe ndiswrapper

# To unload a module

Code:

rmmod nidiswrapper

Compiling your Kernel

# Changes Directory to the current kernel source -- verify the directory with ls -l, and create if necessary with ln -s

Code:

cd /usr/src/linux

# Cleans everything, including config files

Code:

make mrproper

# Reuses the old .config if it exists

Code:

make oldconfig

# or xconfig or gconfig, depending on personal preference

Code:

make menuconfig

# Creates a compressed kernel image

Code:

make

# Compiles the modules

Code:

make modules

# Installs the modules

Code:

make modules_install

# Installs the kernel

Code:

make install

Listing and manipulating processes

Listing and manipulating processes

Each process has a unique number, a PID. A list of all running processes is retrieved with ps.

# List of all running processes

Code:

ps -A

# An Extensive list of all running processes

Code:

ps -auxefw

Many handy uses of ps involve a pipe (|) and grep:

# Looks for a process with cron -- may not actually be running, use ps -A for running commands.

Code:

ps axww | grep cron

# an example output -- in this case, cron is not running

Code:

15087 pts/2    R+     0:00 grep --colour=auto cron

# Finds all ssh PIDs without the grep pid

Code:

ps aux | grep 'ss[h]'

# Find the PIDs of processes by (part of) name

Code:

pgrep -l sshd

# Echos the PID of your shell

Code:

echo $$

# List processes using port 22 on TCP

Code:

fuser -va 22/tcp

# List processes accessing the /home partiton

Code:

fuser -va /home

# Trace system calls and signals

Code:

strace df

# Display the last 50 used commands

Code:

history | tail -50

Priorities

Change the priority of a running process with renice. Negative numbers have a higher priority,
the lowest is -20 and "nice" have a positive value.

# Stronger priority on PID 1070

Code:

renice -5 1070

# Output would look something like the following:

Code:

1070: old priority 0, new priority -5

Start the process with a defined priority with nice. Positive is "nice" or weak,
negative is strong scheduling priority. Make sure you know if /usr/bin/nice or
the shell built-in is used (check with which nice).

# Stronger priority (/usr/bin/nice)

Code:

nice -n -5 top

# Weaker priority (/usr/bin/nice)

Code:

nice -n 5 top

# tcsh builtin nice (same as above)

Code:

nice +5 top

While nice changes the CPU scheduler, an other useful command ionice will schedule the disk IO.
This is very useful for intensive IO application which can bring a machine to its knees while
still in a lower priority. You can select a class (idle - best effort - real time),
the man page is short and well explained.

# set idle class for pid 123

Code:

ionice c3 -p123

# Run firefox with best effort and high priority

Code:

ionice -c2 -n0 firefox

# Set the actual shell to idle priority

Code:

ionice -c3 -p$$

For example, the last command is very useful to compile or debug a large project.
Every command launched from this shell will have a lower priority and will not disturb the system.
$$ is your shell pid (use echo $$ to see the PID of your shell.).

Background/Foreground

When started from a shell, processes can be brought in the background and back to the foreground with <Ctrl>-<Z> (^Z),
bg and fg. For example start two processes, bring them in the background, list the processes with jobs and bring one
in the foreground.

Code:

ping google.com > ping.log

# ping is suspended (i.e stopped) with <Ctrl>-<Z>

Code:

^Z

# put in background and continues running

Code:

bg

# List processes in background

Code:

jobs -l

# example output:

Code:

[1]  - 36232 Running                       ping google.com > ping.log
[2]  + 36233 Suspended (tty output)        less /var/log/messages

# Bring process number 2 back in foreground

Code:

fg %2

Use nohup to start a process which has to keep running when the shell is closed (it is immune to hangups).

# Also needs the '&' to sub-task the ping

Code:

nohup ping -i 60 > ping.log &

Using top effectively

The program top displays running information of processes.

# runs top from the terminal

Code:

top

While top is running press the key h for a help overview. Useful keys are:

* u [user name] To display only the processes belonging to the user. Use + or blank to see all users

* k [pid] Kill the process with pid.

* 1 To display all processors statistics (Linux only)

* R Toggle normal/reverse sort.

Signals/Kill

Terminate or send a signal with kill or killall. Kill kills something with a PID, killall with the process name, see
man kill and man killall for more info.

Code:

ping -i 60 google.com > ping.log &

#PID of the ping process

Code:

[1] 4712

# same as kill -15 4712

Code:

kill -s TERM 4712

# Kill HUP processes by exact name

Code:

killall -1 httpd

# Kill TERM processes by (part of) name

Code:

pkill -9 http

# Kill TERM processes owned by www

Code:

pkill -TERM -u www

# Kill every process accessing /home (to umount)

Code:

fuser -k -TERM -m /home

Important signals are (use anything above signal 3 with caution):

* 1 HUP (hang up)

* 2 INT (interrupt)

* 3 QUIT (quit)

* 9 KILL (non-catchable, non-ignorable kill)

* 15 TERM (software termination signal)

File Systems
Permissions

Change permission and ownership with chmod and chown.
The default umask can be changed for all users in /etc/profile.
The default umask is usually 022. The umask is subtracted from 777,
thus umask 022 results in a permission 0f 755:

1 --x execute # Mode 764 = exec/read/write | read/write | read
2 -w- write # For: |-- Owner --| |- Group-| |Oth|
4 r-- read
ugo=a u=user, g=group, o=others, a=everyone

# MODE is of the form [ugoa]*([-+=]([rwxXst]))

Code:

chmod [OPTION] MODE[,MODE] FILE

# Restrict some-log -rw-r-----

Code:

chmod 640 /var/log/some-log

# Same as above

Code:

chmod u=rw,g=r,o= /var/log/some-log

# Recursive remove other readable for all users

Code:

chmod -R o-r /home/*

# Set SUID bit on executable (use with caution)

Code:

chmod u+s /path/to/app

# Find all programs with the SUID bit

Code:

find / -perm -u+s -print

# Change the user and group ownership of a file

Code:

chown user:group /path/to/file

# Change the group ownership of a file

Code:

chgrp group /path/to/file

# Change permissions to 640 for all files

Code:

chmod 640 `find ./ -type f -print`

# Change permissions to 751 for all directories

Code:

chmod 751 `find ./ -type d -print`

Disk information

# information about the IDE/ATA disk

Code:

hdparm -I /dev/sda

# Display and manipulate the partition table

Code:

fdisk /dev/sda

# Display the disk SMART info (must have a SMART compatible disk) -- install with apt-get install smartmontools

Code:

smartctl -a /dev/sda

System mount points

# Show mounted file-systems on the system

Code:

mount | column -t

# display free disk space and mounted devices (use -h to show in human readable format)

Code:

df

# Show all registered partitions

Code:

nano -w /proc/partitions

Disk usage

# Directory sizes as listing

Code:

du -sh *

# Total directory size of the current directory

Code:

du -csh

# Sort everything by size in kilobytes

Code:

du -ks * | sort -n -r

# Show files, biggest last

Code:

ls -lSr

Find out who has which files opened

This is useful to find out which file is blocking a partition which has to be unmounted and gives a typical error of:

# umount impossible because a file is locking home

Code:

umount /home/
umount: unmount of /home 
failed:    Device busy

A lot of linux OSs can use fstat for this sort of thing, ubuntu appears not to have it, i will look for another tool for this

Find opened log file (or other opened files), say for your Xorg log file:

Code:

ps ax | grep Xorg | awk '{print $1}'

#example output:

Code:

The file with inum 212042 is the only file in /var:

Code:

find -x /var -inum 212042

# example ouptut:

Code:

/var/log/Xorg.0.log

Find opened files on a mount point with fuser or lsof:

# List processes accessing /home

Code:

fuser -m /home

Code:

lsof /home

#example output:

Code:

COMMAND   PID    USER   FD   TYPE DEVICE    SIZE     NODE NAME
tcsh    29029 joe  cwd    DIR   0,18   12288  1048587 /home/joe (guam:/home)
lsof    29140 joe  cwd    DIR   0,18   12288  1048587 /home/joe (guam:/home)

About an application:

Code:

ps ax | grep Xorg | awk '{print $1}'

# example output:

Code:

lsof -p 3324

#example output

Code:

COMMAND   PID    USER   FD   TYPE DEVICE    SIZE    NODE NAME
Xorg    3324 root    0w   REG        8,6   56296      12492 /var/log/Xorg.0.log

About a single file:

Code:

lsof /var/log/Xorg.0.log

# example output

Code:

COMMAND  PID USER   FD   TYPE DEVICE  SIZE  NODE NAME
Xorg    3324 root    0w   REG    8,6 56296 12492 /var/log/Xorg.0.log

Mount/remount a file system

For example, mounting your cdrom drive. If it is listed in /etc/fstab:

Code:

mount /dev/cdrom

if not

# typical ubuntu cdrom mount command

Code:

mount -t auto /dev/cdrom /media/cdrom

# typical IDE

Code:

mount /dev/hdc -t iso9660 -r /media/cdrom

# typical SCSI cdrom

Code:

mount /dev/scd0 -t iso9660 -r /media/cdrom

# typical SCSI -- must have ntfs-3g tool installed either install with apt-get

Code:

mount /dev/sdc0 -t ntfs-3g /media/windows

# or you could swap ntfs-3g with ntfs if you have the ntfs kernel module installed.

Code:

mount /dev/sdc0 -t ntfs /media/windows

Entry in /etc/fstab:

Code:

/dev/cdrom   /media/cdrom  auto noauto,fs=cdfss,ro,procuid,nosuid,nodev,exec 0 0

Remount

Remount a device without unmounting it. Necessary for fsck for example

Code:

mount -o remount,ro /

Copy the raw data from a cdrom into an iso image:

Code:

dd if=/dev/cdrom of=file.iso

Add swap on-the-fly

Suppose you need more swap (right now), say a 2GB file /swap2gb.

Code:

dd if=/dev/zero of=/swap2gb bs=1024k count=2000

# create the swap area

Code:

mkswap /swap2gb

# activate the swap.

Code:

swapon /swap2gb

# when done deactivate the swap

Code:

swapoff /swap2gb

# remove the swap

Code:

rm /swap2gb

Mount a samba share

Suppose we want to access the SMB share myshare on the computer smbserver,
the address as typed on a Windows PC is \\smbserver\myshare\.
We mount on /mnt/smbshare. Warning> cifs wants an IP or DNS name, not a Windows name.

# List the shares

Code:

smbclient -U user -I 192.168.16.229 -L //smbshare/

Code:

mount -t smbfs -o username=winuser //smbserver/myshare /mnt/smbshare

Code:

mount -t cifs -o username=winuser,password=winpwd //192.168.16.229/myshare /mnt/share

Additionally with the package mount.cifs it is possible to store the credentials
in a file, for example /home/user/.smb:

username=winuser
password=winpwd

And mount as follow:

Code:

mount -t cifs -o credentials=/home/user/.smb //192.168.16.229/myshare /mnt/smbshare

Mount an image

# Mount a CD image

Code:

mount -t iso9660 -o loop file.iso /mnt/image

# Mount an image with ext3 fs[code]mount -t ext3 -o loop file.img /mnt/image [/code]Create and burn an ISO image

This will copy the cd or DVD sector for sector. Without conv=notrunc,
the image will be smaller if there is less content on the cd.
See below and the dd examples.

Code:

dd if=/dev/cdrom of=/tmp/mycd.iso bs=2048 conv=notrunc

Use mkisofs to create a CD/DVD image from files in a directory.
To overcome the file names restrictions: -r enables the Rock Ridge
extensions common to UNIX systems, -J enables Joliet extensions used
by Microsoft systems. -L allows ISO9660 filenames to begin with a period.

Code:

mkisofs -J -L -r -V TITLE -o imagefile.iso /path/to/dir

Also use cdrecord with Linux as described above. Additionally it is possible to
use the native ATAPI interface which is found with:

Code:

cdrecord dev=ATAPI -scanbus

And burn the CD/DVD as above.
dvd+rw-tools

The dvd+rw-tools package can do it all and includes growisofs to burn CDs or DVDs.
The examples refere to the dvd device as /dev/dvd which could be a symlink to /dev/scd0
(typical scsi on Linux), although you will probably want /dev/cdrom.

# -dvd-compat closes the disk
# Burn existing iso image

Code:

growisofs -dvd-compat -Z /dev/dvd=imagefile.iso

# Burn directly

Code:

growisofs -dvd-compat -Z /dev/dvd -J -R /p/to/data

Convert a Nero .nrg file to .iso

Nero simply adds a 300Kb header to a normal iso image. This can be removed with dd.

# Backup .nrg file first before doing this just in-case

Code:

dd bs=1k if=imagefile.nrg of=imagefile.iso skip=300

Convert a bin/cue image to .iso

The little bchunk programhttp://freshmeat.net/projects/bchunk/ can do this.
Can install from the ubuntu repos with sudo apt-get install bchunk

Code:

bchunk imagefile.bin imagefile.cue imagefile.iso

Create a file based image

Code:

dd if=/dev/zero of=/usr/vdisk.img bs=1024k count=1024

Code:

mkfs.ext3 /usr/vdisk.img

Code:

mount -o loop /usr/vdisk.img /mnt/mountpoint

# Cleanup

Code:

umount /mnt; rm /usr/vdisk.img

Linux with losetup

/dev/zero is much faster than urandom, but less secure for encryption.

Code:

dd if=/dev/urandom of=/usr/vdisk.img bs=1024k count=1024

# Creates and associates /dev/loop0

Code:

losetup /dev/loop0 /usr/vdisk.img

Code:

mkfs.ext3 /dev/loop0

Code:

mount /dev/loop0 /mnt

# Check used loops

Code:

losetup -a

Code:

umount /mnt

# Detach

Code:

losetup -d /dev/loop0

Code:

rm /usr/vdisk.img

Create a memory file system

A memory based file system is very fast for heavy IO application. How to create a 64 MB partition mounted on /memdisk:

Code:

mount -t tmpfs -osize=64m tmpfs /memdisk

Disk performance

Read and write a 1 GB file on partition sda2 (/home)

Code:

time dd if=/dev/sda2 of=/dev/null bs=1024k count=1000

Code:

time dd if=/dev/zero bs=1024k count=1000 of=/home/1Gb.file

Code:

hdparm -tT /dev/hda

Happy Ubuntuing

**Rocket2DMn** · June 27th, 2008

Debian runlevels are a little different than other linux runlevels, you may want to add info about that.
Also, take out the info about (re)setting root password, see http://ubuntuforums.org/showthread.php?t=765414
You may consider adding links to help wiki pages as well.

**ajmorris** · June 28th, 2008

Originally Posted by Rocket2DMn

Debian runlevels are a little different than other linux runlevels, you may want to add info about that.

Tks, added

Also, take out the info about (re)setting root password, see http://ubuntuforums.org/showthread.php?t=765414

Done, and thanks, dont want this getting jailed

**jakupl** · June 28th, 2008

Great stuff, but why don't you use the [CODE] envelopes?

**ajmorris** · June 28th, 2008

Originally Posted by jakupl

Great stuff, but why don't you use the [code] envelopes?

I will if you wish

That looks much better... i will do the rest later, i have to leave right now

**jakupl** · June 28th, 2008

Only if you like.

However thanks a bunch for making this.

**Oldsoldier2003** · June 28th, 2008

Good job AJ, a nice resource for beginners and a handy refresher for folks that have been around awhile

**Oldsoldier2003** · June 28th, 2008

Code:

who -b

shows the last system boot time.

Code:

cat /etc/debian_version

will return the Debian version without opening nano.

**ajmorris** · June 28th, 2008

Originally Posted by Oldsoldier2003

Code:

who -b

shows the last system boot time.

Code:

cat /etc/debian_version

will return the Debian version without opening nano.

Added/changed

There will be lots where i used nano that you could use cat or less to view without opening ... I already changed them all from what i had before (vim) to nano... then realised that vim comes standard with ubuntu as well

**NekoCodi** · June 30th, 2008

Yeah AJ, thanks man. I'll defnitely get a lot of use out of this!

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