ITR3 lecture 8: more UNIX, DNS and mail Thomas Krichel

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 badblockscheck disk for bad blocks on disk cfdiskdisk partitioning tool e2fsckfile system checking tool initinitial program insmodinsert module in kernel kbdrateset keyboard rate important! kernelversionshows version of kernel

Other important system binaries liloinstalls loading lsmodshows modules mke2fsdisk formatting pumpsimple dhcp client shutdownshut down machine swaponswap dateshows if you have a date hostnameshows host name mvmoves files

Other utilities pwd shows the current directory passwdsets password tar archiver dselectdebian package installer basenamebase name of a file clearclears screen cutcuts text diffdifference 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 = 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

Example openlib.org. IN SOA wotan.liu.edu. tkrichel.wotan.liu.edu. ( ; Serial ; Refresh after 3 hours 3600 ; Retry after 1 hour ; Expire after 1 week ; 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 fasolt.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.

Thank you for your attention!