CONNECTIVITY

exit

- end current shell process. If you log in, then type this command, it will return you to login. ^D (control-D) and logout (in some shells) does the same.

rlogin

- login to a remote machine, e.g.
$ rlogin hollandrs # log in to machine called hollandrs
Useful with -l option to specify username - e.g.
$ rlogin cityrs -l ismsdev # log in to machine cityrs as user ismsdev For further info about trust network see .rhosts file and /etc/resolv.conf (I think).

telnet

- very similar to rlogin except that it is more flexible (just type telnet with no arguments and then '?' to see the options). Useful because you can specify a telnet to a different port.

ftp

- File Transfer Protocol - a quick and easy method for transferring files between machines. The .netrc file in your $HOME directory holds initial commands. type ftp without arguments and then '?' to see options)

rcp

- Remote copy. Copies a file from one unix box to another, as long as they trust each other (see .rhosts file or /etc/resolv.conf I think). Options

• -f (to force the copy to occur)
• -r (to recursively copy a directory)
• -p (to attempt to preserve permissions when copying)

su -

- switch user, option '-' means that the users .profile is run, without option you merely assume the id and permissions of the user, without (for example) changing PATH and DBPATH, e.g.
$ su - root # become root
$ su root # gain permissions of root but don't change the current environment variables
$ su - vlink # switch to user vlink
If you are root, you may su to any other user without being prompted for a password. su without arguments is the same as 'su root'. Note that the 'su' option is not available on all UNIX machines as it can crash some of them.

ping 

- check that is alive and well (do not expect an immediate response from a machine that is linked over an ISDN line). Firewalls often block ping packets after the Ping of Death so quite often you'll find you can't ping internet sites either. Options include:

• -q ping quietly
• -i wait no of seconds between each packet sending. The default is 1 second. If you are using ping to keep an ISDN line up then using something like $ ping -i 5 -q hollandrs is ideal.
• -f Never use this! Sends as many packets as it possibly can as fast as possible, used for network debugging and is likely to slow networks horribly when used. Known as 'flood' pinging.
• -c send no of packets before giving up

To check that your machine can ping, try pinging 127.0.0.1 - this acts as a feedback loop, checking the network card's ability to ping.

rsh 

- remote shell - e.g.
$ rsh altos more /tmp/chk # will run the command more the file /tmp/chk on the machine called altos. Useful in pipes for example. rsh on its own will execute a login. Use option '-l' to specify logon name. You can also use rcmd and remsh on other flavours of unix.

host 

- lookup the ip address in the /etc/hosts file and give its name