ITR3 lecture 8:more UNIX, DNS and mail

Thomas Krichel

2002-11-05

Directory tree I• /bin Essential command binaries

• /boot Static files of the boot loader

• /dev Device files

• /etc Host-specific system configuration

• /home User home directories

• /lib Essential shared libraries and kernel modules

• /mnt Mount point for mounting a file system temporarily

Directory tree II

• /proc Virtual directory for system information

• /root Home directory for the root user • /sbin Essential system binaries • /tmp Temporary files • /usr Secondary hierarchy • /var Variable data • /opt Add-on application software packages

The kernel

• is /vmlinuz

• Note that this is a symlink, set by lilo

• It is supplemented by a number of modules that can be on and offloaded.

• Modules live in /lib/modules

• modconf can be used to add and remove modules.

Important System binaries• badblocks check disk for bad blocks on

disk• cfdisk disk partitioning tool• e2fsck file system checking tool• init initial program• insmod insert module in kernel• kbdrate set keyboard rate important!• kernelversion shows version of kernel

Other important system binaries• lilo installs loading• lsmod shows modules• mke2fs disk formatting• pump simple dhcp client• shutdown shut down machine

• swapon swap • date shows if you have a date• hostnameshows host name• mv moves files

Other utilities

• pwd shows the current directory• passwd sets password• tar archiver• dselect debian package installer• basename base name of a file• clear clears screen• cut cuts text • diff difference between files

processes

• A software that is running on a machine is called a process.

• top is a utility to see what processes are running and who is running them.

• Kill -9 number kills the process.• If the process is a daemon, it is best to use

/etc/init.d/daemon stop so that it exits gracefully.

• Start again with /etc/init.d/daemon restart

compression

• Some files are held in compressed form.

• On Linux machines, zip-lempel is popular, files that are compressed in this way have an extension .gz.

• Use gzip to create compressed files.

• Use gunizip file.gz to uncompress a file

• Use zcat file.gz to display an uncompressed file.

File editing

• Emacs is a large file editor used by geeks.

• For beginners, nano is better.

• Nano is a pico clone available under the GPL.

• The commands available are being displayed in the menu

• ^C where I is a letter, means pressing I and control at the same time.

ntp

• Is the network time protocol, used to make sure that the time that you have an a machine is the same correct.

• The correct time is given to you by a server. A list of public servers is given on a web page

• Use /etc/init.d/ntp to install ntp properly. • Get a use a public time server and add its name

as a server where to get the time from

DNS

• A host name associates a human-friendly name with an IP address.

• Example: trabbi.liu.edu = 148.4.16.229• Finding an IP for a name is called a name

lookup. The reverse is a reverse lookup.• Names are a sequence of labels, separated by

dot.• Names may contain letters, numbers and

hyphens. They may not start with a hyphen.• Names solve from right to left, contrary to

addresses, that resolve from left to right.

purpose

• Allows to keep constant name for– changing machines– changing the location of the machine.

• Makes it easier for humans to remember access points to services.

• Establish brand names and have an economic value

History of DNS

• In the 70s, one single file HOSTS.TXT was maintained at SRI-NIC, downloaded frequently by all hosts on the Internet.

• Problems– traffic and load– name collisions– Consistency

• 1984, Paul Mockapetris releases RFC822 and RFC883 that describe the Domain Name System DNS.

• First implementation software called JEEVES.

ddclient

• Allows you to get a domain name despite changing IP address.

• Open an account with dyndns.org, get password.

• Then go to “create new host”

• Enter data that is requested.

• Enter data on the client in /etc/ddclient

• Start ddclient /etc/init.d/ddclient start

DNS and domains

• DNS is– distributed database– client server architecture– general purpose– hierarchical structure– independent of physical structure

Berkeley Internet Name Domain

• BIND is an implementation of the Domain Name System (DNS) protocols and provides an openly redistributable reference implementation of the major components of the Domain name system, including– a Domain Name System server (named)– a Domain Name System resolver library– tools for verifying the proper operation of the

DNS server

Exampleopenlib.org. IN SOA wotan.liu.edu. tkrichel.wotan.liu.edu. ( 2001111300 ; Serial 10800 ; Refresh after 3 hours 3600 ; Retry after 1 hour 640800 ; Expire after 1 week 86400 ; Minimum ttl of 1 day)openlib.org. IN NS wotan.liu.edu.; primary server, the one which holds the authoritative info (this file)openlib.org. IN NS utserv.mcc.ac.uk.; secondary servers -- if they are willing to be. At least one is

necssesary.openlib.org. IN A 131.227.9.154fasolt.openlib.org IN CNAME wotan.liu.edu.openlib.org. IN MX 1 wotan.liu.edu.trabbi.openlib.org. IN TXT "hello world"

Mail configuration

• Exim is the default mailer on Debian.

• Use exim_config to configure it.

• Use to handle mail for your domain only, don’t relay mail for other domain, this could be problematic.

• If you want to configure mailman for mailing list, you will have to manually edit the exim.conf file.

mutt• "All mail clients suck. This one just sucks

less." creator of mutt, circa 1995

• System wide configuration /etc/Muttrc

• /home/user/.muttrc overwrites this system-wide features.

• You may wish to set the editor to nano before mailing.

• Generally, an extremely configurable software.

http://openlib.org/home/krichel

Thank you for your attention!