Course

At CSL on 16th November 2004

Debian

Stable
Unstable

Gentoo

http://www.gentoo.org/
Portage
Frequently updated
Can emerge an old or a new version
Can run different versions of the same package
Can use one machine to compile the binaries and distribute to all the other machines.

Choice of kernel

2.4 or 2.6
We will use 2.6

Configuration often stored in /etc/conf.d/

Initialisation is often stored in /etc/init.d/

Software RAID - Try the following pages for help:

Useful Commands

Hold down Alt, SysRq while you type K, S, U, B

K - Kills all running disks
S - Synchronises drives
U - umounts drives
B - reboot

Note: On the Microsoft Natural Multimedia Keyboard you need to switch off “F Lock”, Hold down “Ctrl” and then press Alt SysRq etc…

Shift - Page Up and Page Down - will allow you to scroll back through screens.

cp/mv

Copy/Move

chmod

Make something executable

chmod +x <filename>
chmod +r <filename> to make read only for the current user

less

Check the system log:
```
less /var/log/messages
```
ls

Long listing of everything
```
ls -la
```
Sort by date/time
```
ls -last

<<<lsof>>>
```
list open files - shows the port as well
```
lsof | less
```
cron

To edit a crontab:
```
crontab -e
```
du

To find out how much disk space is used in the current folder and the ones below:
```
du -ch
```
Disk Usage - End of listing shows a summary

grep

cat /var/log/messages | grep -i warning - -i = ignore case

less

Similar to more on windows - but you can scroll back up!

zless

Same as more - but will work on compressed files.
locate

To install
```
emerge slocate
```
- a utility which will check the whole hard disk each day and store a map of the file system for quick searches
- to update the locate database
```
updatedb &
```
to search the database
```
locate <search>
```

lsof

Utilities for viewing which ports and network services are open/running

lsof (list open files)
lsof | grep -i listen
cat /etc/services | grep pop

make

the compiler will use inter process communications
```
-pipe
```
another register for the compiler - debug stack trace is not useful.
```
-fomit-frame-pointer
nano -w /etc/make.conf.example
```
We could compile binaries in Crediton, upload them to a web site and all sites could download from this location
```
PORTAGE_BINHOST
```
mkdir

To make a directory.
mount
- Mount a CDROM
- If the file system you want is already mentioned in fstab then just:
```
mount /mnt/cdrom
```
- To unmount:
```
umount /mnt/cdrom
```
- If not in fstab
```
cat /proc/devices
```
- Use command completion to choose device:
```
mount /dev/<device e.g. hdd> /mnt/cdrom
```
  hd = ide, b = scsi
nano
- Is a clone of pico - easy to use - installed by default on Gentoo.
- -w turns off word wrap
- Always use -w to switch off word wrap
- NOTE - It saves the file word wrapped if you do not switch off word wrap.
nmap
- Simple port scanning:
```
nmap <ip address> -O
```
  To display OS details:
```
-O
```
  loopback - scan yourself or my ip address:
```
nmap -sT -vvv 127.0.0.1
```
See lsof
ps
- processes
- show original command line
- a - all tasks
- x - list services as well
- u - all users
```
ps faux | less - f
kill -9 <pid>
```
shows processes
```
top
```
- nice level - +19 is the lowest priority
- wa is the CPU wait time - if it goes high then investigate faster hard drives
- load average - usually around 2
If a thread is blocking IO then it will add a whole 1 to the load average A zombie process could be a bad thing - Press the </> keys to change the sort order, ? to get help
pstree

Gives an idea of what is currently running
Ctrl Z pauses in the background
bg lets the task continue in the background
fg brings the task into the foreground
jobs - will list what you have in the background
%1 to the first task
To launch in the background add an & to the end of the command
rmdir
screen

Allows you to control multiple screens on a remote Linux computer. Like terminal server for Linux consoles. emerge -v screen screen