ITR3 lecture 9:DNS, mail, rsync

Thomas Krichel

2002-11-05

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 two RFCs that describe the Domain Name System DNS.

• First implementation software called JEEVES.

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"

/etc/hosts

• Poor-man’s DNS

• You can list names and IP addresses. These are sometimes used before DNS is queried.– Opera does that– Lynx does not do it

• Check your /etc/hosts when you have weird DNS problems.

/etc/resolv.conf

• Configures the resolution of names. • Usual commands

– nameserver ip_address names a name server to be queried at an ip address to resolve name. This may not be necessary with dynamic ip addressing, the dhcp server usually names a name server.

– search domain says to search a domain for a certain name. Thus “search liu.edu” allows you to say “slogin wotan” instead of “slogin wotan.liu.edu”

Mail configuration

• Exim is the default mailer on Debian.• Use eximconfig to configure it (better), or

edit /etc/exim/exim.conf• 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.

/etc/aliases

• A simple file to configure aliases for the delivery of mail

• Most of the time, used for local users

• Can also support comma-separated lists of remote users, thus a poor-man’s mailing list service

/etc/passwd

• Does not contain passwords, usually. Nowadays they are kept in /etc/shadow, for some security reason.

http://openlib.org/home/krichel

Thank you for your attention!