Lazy Linux: essential tricks for admins • Hacker News Board

Re: Lazy Linux: essential tricks for admins

#41

Post by decode » Fri, Jan 16, 2009, 5:22 PM UTC

delano wrote: post #39

khafra wrote: post #38

Earlier quoted context omitted.

The primary bootloaders for Linux distributions are http://en.wikipedia.org/wiki/GNU_GRUB and http://en.wikipedia.org/wiki/LILO_(boot_loader) with a large edge in popularity to GRUB these days. Unless it's a fork or modification, GRUB works like this: http://www.gnu.org/software/grub/manual Single User Mode isn't unique to CentOS/Redhat, or even Linux. In fact, the concept behind it isn't even unique to Unix: One of…

I'm aware of GRUB and LILO. But as bootloaders, I didn't realize they were able to modify the Linux root password so easily. The question still stands: is it possible in any flavour of Linux to change the root password by modifying the kernel parameters at boot-time?

On any flavor of linux that uses GRUB or LILO it's possible to modify the kernel parameters at boot time to enter single-user mode. Once you're in single-user mode you have full root privileges and environment and can change any passwords or files you like.

Re: Lazy Linux: essential tricks for admins

#42

Post by ionfish » Fri, Jan 16, 2009, 5:42 PM UTC

khafra wrote: post #37

ionfish wrote: post #18

Earlier quoted context omitted.

My general attitude to passwords is "Never choose something you'd be ashamed to recite to your mother over the phone", since you never know when you'll be in a position where you may have to do exactly that.

As an information assurance guy, I'd encourage users to use the most embarassing possible passwords, since you should never share them. If you need to make resources available to more entities, do it by sharing access, not authentication.

Generally speaking I agree with you, but in the real world (with real users!) this is not always possible.

Re: Lazy Linux: essential tricks for admins

#43

Post by delano » Fri, Jan 16, 2009, 5:47 PM UTC

decode wrote: post #41

delano wrote: post #39

Earlier quoted context omitted.

I'm aware of GRUB and LILO. But as bootloaders, I didn't realize they were able to modify the Linux root password so easily. The question still stands: is it possible in any flavour of Linux to change the root password by modifying the kernel parameters at boot-time?

On any flavor of linux that uses GRUB or LILO it's possible to modify the kernel parameters at boot time to enter single-user mode. Once you're in single-user mode you have full root privileges and environment and can change any passwords or files you like.

Ah, okay. Thanks for explaining that. I didn't realize it was possible to get into single user mode without the password for any Linux.

Is the same true for BSDs, Solaris, et al?

Re: Lazy Linux: essential tricks for admins

#44

Post by decode » Fri, Jan 16, 2009, 7:00 PM UTC

delano wrote: post #43

decode wrote: post #41

Earlier quoted context omitted.

On any flavor of linux that uses GRUB or LILO it's possible to modify the kernel parameters at boot time to enter single-user mode. Once you're in single-user mode you have full root privileges and environment and can change any passwords or files you like.

Ah, okay. Thanks for explaining that. I didn't realize it was possible to get into single user mode without the password for any Linux. Is the same true for BSDs, Solaris, et al?

I've never tried it on anything but linux, but it looks like it's common:

FreeBSD: http://www.cyberciti.biz/tips/howto-freebsd-reset-recover-ro...

OpenBSD: http://www.openbsd101.com/tipstricks.html#tt1

Solaris: http://www.cyberciti.biz/tips/solaris-boot-system-into-singl...

Re: Lazy Linux: essential tricks for admins

#45

Post by marbletiles » Sat, Jan 17, 2009, 12:09 AM UTC

# while [ 1 ]; do echo "All your drives are belong to us!"; sleep 30; done

Hee, things I didn't think I'd ever see on ibm.com, #12234 in a series.

People with company songbooks and nice ties must be spinning in their graves

Re: Lazy Linux: essential tricks for admins

#46

Post by d0mine » Sat, Jan 17, 2009, 2:39 AM UTC

palish wrote: post #19

xelfer wrote: post #17

Earlier quoted context omitted.

lsof, ngrep, history (only found out this one a month ago after 6 years of being a sysadmin)

What terrible names. Sorry, but from a non-Unix perspective, symbols such as 'lsof' and 'ngrep' seem arbitrary and nonsensical.

They are derivatives of very well known names in Unix: ls and grep.

When ls utility was created standard RAM was 10KB and power computers looked like this http://images.appleinsider.com/leopard-preview-server-1.jpg

I guess if your IO interface is a real dead-tree paper then each character counts.

Re: Lazy Linux: essential tricks for admins

#47

Post by d0mine » Sat, Jan 17, 2009, 2:46 AM UTC

11ren wrote: post #31

tome wrote: post #25

Earlier quoted context omitted.

palish has a point to the extent that lsof is so infrequently used that it would do no harm to give it a more descriptive name. Nonetheless, I entirely agree with you about ls, and about sticking to the conventions that have developed around unix.

There's a tribal aspect, too; not to mention jargon as a barrier to entry. And what professional wants to forgo hard-won knowledge? That said, I kind of like the weird names, esp grep. (Wasn't that in Stranger in a Strange Land or something?) But I do object to inconsistent options. One example is: mkdir -p a/b/c This will make all three nested directories, if needed; but there is no equivalent: mv -p x a/b/c/y There…

Inconsistent options are like irregular verbs in English (the most frequently used verbs are both ancient and irregular as a rule).

Re: Lazy Linux: essential tricks for admins

#48

Post by Xichekolas » Sat, Jan 17, 2009, 6:59 AM UTC

khafra wrote: post #37

ionfish wrote: post #18

Earlier quoted context omitted.

My general attitude to passwords is "Never choose something you'd be ashamed to recite to your mother over the phone", since you never know when you'll be in a position where you may have to do exactly that.

As an information assurance guy, I'd encourage users to use the most embarassing possible passwords, since you should never share them. If you need to make resources available to more entities, do it by sharing access, not authentication.

This is what I love about Hacker News... even a semi-trollish post generates two great replies that I am glad to have read.

Re: Lazy Linux: essential tricks for admins

#49

Post by easyrider2 » Sat, Jan 17, 2009, 7:09 AM UTC

m0nty wrote: post #32

To get back a hosed screen, also try: stty sane ^j (That's Ctrl-j there.) You might be flying blind, but just do it and you might get your screen back. You probably know this, but to rescue a hosed system with Knoppix or similar live-cd: - Boot from CD. - Open root console. - Mount your usual root partition: mount -t somefs /dev/hda1 /mnt/oldsys - chroot /mnt/odlsys /bin/bash Showed that to another admin who'd lost a…

A detailed article on rescuing a hosed system with Knoppix:

How Knoppix saved the day

http://www.dancingbison.com/writings/knopresc.txt

Re: Lazy Linux: essential tricks for admins

#50

Post by 11ren » Sat, Jan 17, 2009, 11:10 AM UTC

gaius wrote: post #34

11ren wrote: post #31

Earlier quoted context omitted.

There's a tribal aspect, too; not to mention jargon as a barrier to entry. And what professional wants to forgo hard-won knowledge? That said, I kind of like the weird names, esp grep. (Wasn't that in Stranger in a Strange Land or something?) But I do object to inconsistent options. One example is: mkdir -p a/b/c This will make all three nested directories, if needed; but there is no equivalent: mv -p x a/b/c/y There…

Grok, you're thinking of.

yes! thanks,