I’ve learned almost everything I know about UNIX on my own, and even when I’ve been shown how to do something from the command line, troubleshooting often puts me on the path of self-instructed discovery. Here are some tools I use a lot (specifically in OS X), when mapping uncharted territory.sudo – type this before a command to ‘do’ it as the superuser (root).
apropos – this command helps you locate commands and files related to a search term you enter. ‘apropos password’ yields a list of commands for working with different types of passwords, etc.
man – follow this command with the name of a command you don’t know anything about – you get a manual (man) page abou the command.
ls -la – with the ‘-la’ variable you see the listed (ls) contents of a directory with details on permissions. you also see hidden files and directories.
mkdir – make a new directory/folder
chmod – change the permissions for a file/folder
chown – change the owner for a file/folder
chgrp – change the group for a file/folder
rm – remove a file/folder (-r flag remove all file and subfolders in a folder recursively).
nslookup – deprecated in favor of ‘dig,’ but very simple to use when debugging dns. type ‘server’ at the prompt to see you dhcp and manually-supplied dns servers, and the dns name of a machine on the network to see if you get full resolution.
ping – of course used to see if a link is up, but also useful to see if there is a dns entry for a host. type ‘ping example.domain.suffix’
ssh – the best way to connect to a far-away machine – only requires one open port in a firewall, and connects via encrypted tunnel. enabled by default on OSX Server. best syntax is like this: ‘ssh -2 [email protected]’
shutdown – a kinder, gentler version of the brutal ‘halt’ command. ‘shutdown -r now’ reboots a server fairly smoothly. ‘shutdown -h now’ shuts it down likewise. read the man page for more goodies.
dscl – tough to use, but a good way to troubleshoot open directory issues. READ the man for this one!
softwareupdate – a good command to run is ‘sudo softwareupdate -i -r’ – this install all required updates. be aware that you have to ‘sudo shutdown -r now’ afterwards…
system_profiler – does just what it says – but the output is VERY long, so use…
grep – use to get only what you want from output of a command (means ‘grab regular expression’) – a simple use would be ‘system_profiler | grep Machine’. case-sensitive.
top – list processes and their cpu load, memory state, etc. ‘top -u’ put the most expensive processes at the top. useful in conjunction with…
kill – terminate processes by their id numbers – id numbers are listed to the left of the process in output from ‘top’. example – ‘kill 1492’. adding -9 flag is sort of like swatting a gnat with a sledgehammer; sometimes its just more fun that way.
mv – use to move or rename file/folder. example of renaming: ‘mv foo.txt foo-foo.txt’ – foo.txt becomes foo-foo.txt.
cp – copies file or folder (with -r flag) to the place you specify
ditto – copies file along with it’s resource fork (with -rsrc flag) – also preserves permissions by default – very useful, read the manpage.
locate – find files containing specified terms. ‘locate secret_passwords.txt’, for example
more – specify a file after this command to view its contents safely (more will not let you make changes).
| – a symbol that means ‘pipe’ – this is one of the truly amazing gut-level features of UNIX. pipes let you send the output of one command to another command as it’s input. see my example for system_profiler. the key for this symbol is just above the return key, if you’ve never used pipes before.
pico – a simple text editor, with easy controls. not as sexy as vi, but (I think) safer if you are not a very skilled vi user. invoke with ‘sudo’ to make changes to system config files and plists.
feel free to reply with your own favorites…
(by the way, i have often found that apropos and locate are broken after a new install – fix this by running two scripts in /usr/libexec – you need the full path. ‘sudo /usr/libexec/locate.updatedb’ and ‘sudo /usr/libexec/makewhatis’)