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ITR3 lecture 9: DNS, mail, rsync

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

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ITR3 lecture 9: DNS, mail, rsync

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  1. ITR3 lecture 9:DNS, mail, rsync Thomas Krichel 2002-11-05

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. DNS and domains • DNS is • distributed database • client server architecture • general purpose • hierarchical structure • independent of physical structure

  8. 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

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

  10. /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.

  11. /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”

  12. 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.

  13. 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.

  14. /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

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

  16. http://openlib.org/home/krichel Thank you for your attention!

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