Do's and Don'ts of Linux

L.Jenkins · 27-09-2014 9:37pm #1

So I thought it might be an idea to start a thread for the provision of some useful tips and tricks. If this has been done to death or it's better to just start a thread and ask, then no worries.

Tonight though, I learned the hard way to not run the following as root or a user regardless

chmod -f -R 777 / | chown -f -R 777 /

Kinet1c · 27-09-2014 11:15pm

Itzy wrote: »

So I thought it might be an idea to start a thread for the provision of some useful tips and tricks. If this has been done to death or it's better to just start a thread and ask, then no worries.

Tonight though, I learned the hard way to not run the following as root or a user regardless

chmod -f -R 777 / | chown -f -R 777 /

I did this very early on too, it was a good lesson to learn

Turning it off and on again tends not to apply with *nix (very rarely imo anyway) as it does with Windows.

L.Jenkins · 28-09-2014 12:08am

I know :P It's a good lesson is shít you don't do, that's why I believe that if you want to try things out, try it out in a VM first.

syklops · 28-09-2014 11:46pm

Less of an issue nowadays but dont login to your desktop environment as root.

If you've not updated bash since last weekend, do it now.

The -y option on yum and I believe Apt-get also, answers yes for all questions. Don't get into the habit of using it by default. There will be a day when removing one library removes your entire desktop.

Use SSH keys. Dont use password-less keys unless its a very low priority system. I use a password-less key on my media centre so I can push stuff to it easily. Thats it. Every other system requires a pass phrase.

L.Jenkins · 29-09-2014 1:54pm

syklops wrote: »

The -y option on yum and I believe Apt-get also, answers yes for all questions. Don't get into the habit of using it by default. There will be a day when removing one library removes your entire desktop...

apt-get upgrade -y

justjustin · 29-09-2014 2:09pm

syklops wrote: »

If you've not updated bash since last weekend, do it now.

Why do you say this? Is this meant as a general "Make sure your bash is up to date" remark, or is it in relation to some issue of late?

I've always used manual upgrading on my linux boxes, apart from when I or someone else may be using a GUI on that box, e.g. HTPC and one laptop.

29-09-2014 2:09pm

Old one, but don't run this in bash/bash-like shell:

:(){ :|: & };:

L.Jenkins · 29-09-2014 2:11pm

Eddie Crooked Muffler wrote: »
Old one, but don't run this in bash/bash-like shell:
:(){ :|: & };:

Dear I ask what hazardous behaviour this will inflict?

syklops · 29-09-2014 2:11pm

justjustin wrote: »

Why do you say this? Is this meant as a general "Make sure your bash is up to date" remark, or is it in relation to some issue of late?

The shellshock vulnerability was reported on Wednesday just gone, its a remote code injection vulnerability(pretty much the worst kind).

justjustin · 29-09-2014 2:12pm

Eddie Crooked Muffler wrote: »
Old one, but don't run this in bash/bash-like shell:
:(){ :|: & };:

Fork off!!

29-09-2014 2:16pm

Itzy wrote: »

Dear I ask what hazardous behaviour this will inflict?

http://en.wikipedia.org/wiki/Fork_bomb

justjustin · 29-09-2014 2:16pm

Itzy wrote: »

Dear I ask what hazardous behaviour this will inflict?

Can't post links.

Google "Linux fork bomb"

L.Jenkins · 29-09-2014 2:24pm

Sounds like fun :P

liamo · 30-09-2014 3:37pm

You could do worse than get into the habit of using screen when you log in over ssh.

I have a script called startScreen.sh in my home directory

#!/bin/bash
if [[ -n $STY ]] ; then
 echo "Already attached to a screen session"
else
 screen -R
fi

I've also added alias r="~/startScreen.sh" to my .bashrc giving me a quick and easy one-key shortcut to creating a new session or re-attaching to an available detached session.
(Yes, "alias s" would be more intuitive but that's already in use)

If you kick off a remote apt-get upgrade or a long compile or other operation it's comforting to know that a dropped connection won't kill your ongoing work or damage your system.

L.Jenkins · 02-10-2014 12:18pm

Depending on how this thread goes, we could nearly put together a mini manual for noobs and novices.

02-10-2014 1:51pm

liamo wrote: »
You could do worse than get into the habit of using screen when you log in over ssh.

I have a script called startScreen.sh in my home directory
#!/bin/bash
if [[ -n $STY ]] ; then
 echo "Already attached to a screen session"
else
 screen -R
fi
I've also added alias r="~/startScreen.sh" to my .bashrc giving me a quick and easy one-key shortcut to creating a new session or re-attaching to an available detached session.
(Yes, "alias s" would be more intuitive but that's already in use)

If you kick off a remote apt-get upgrade or a long compile or other operation it's comforting to know that a dropped connection won't kill your ongoing work or damage your system.

Just an addition to this.

tmux is an alternative to screen.

You can keep commands alive without the use of screen/tmux also if your terminal dies, by launching the command with nohup.

azzeretti · 02-10-2014 2:28pm

Itzy wrote: »

Depending on how this thread goes, we could nearly put together a mini manual for noobs and novices.

I think that's a great idea, the format might have to change a little though.

Quick DO:
Add aliases for potentially dangerous commands especically if coming from Windows, where there are plenty of "Are you sure?" questions afer a command. A simple example is `rm`. By default `rm` will blindy obey however if you add this: alias rm='rm -i' to your .bashrc it will add a bit of security by prompting to confirm your deletion.

You can change to upper case 'I' for prompting to remove many files or recursive command.

liamo · 02-10-2014 3:43pm

Eddie Crooked Muffler wrote: »

tmux is an alternative to screen.

A short Google later .... looks very interesting. New toy to play with this evening.

L.Jenkins · 10-10-2014 12:39pm

Handy little command to get the number of files in a dir:

ls -l . | grep -c '^-'

And if you can't be arsed typing all of that out:

alias numFiles='ls -l . | grep -c '^-''

Then use numFiles instead.

L.Jenkins · 22-10-2014 10:11am

The joy of alias'. They seem to disappear when you close a session. How do you make them stick or save them? Go /home/YourACName/Desktop

ls -a and you'll find .bashrc is in the directory as a hidden file. If you're brave, vi .bashrc and add your alias name='command' to the end of the file. esc :wq to save and exit the file. The alias will remain to use at your convenience.

deconduo · 22-10-2014 4:37pm

Itzy wrote: »

The joy of alias'. They seem to disappear when you close a session. How do you make them stick or save them? Go /home/YourACName/Desktop

ls -a and you'll find .bashrc is in the directory as a hidden file. If you're brave, vi .bashrc and add your alias name='command' to the end of the file. esc :wq to save and exit the file. The alias will remain to use at your convenience.

I thought .bashrc is usually just in the /home/username dir? I've never seen it in /home/username/Desktop before, though that might be the case for some distros.

Sidenote: ~ is short for the current user's home directory. So /home/username/.bashrc could also be written as ~/.bashrc

L.Jenkins · 22-10-2014 4:50pm

You would be right actually, my bad.

Do's and Don'ts of Linux

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