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Can't boot due to permissions error
http://forum.linhes.org/viewtopic.php?f=14&t=15739		 Page 1 of 1
Author:  tzoom84 [ Fri Jun 29, 2007 10:55 am ]
Post subject:  Can't boot due to permissions error
I've successfully been able to install KnoppMyth and starting adding and configuring some additional utilities for fun.

Unfortunately, I believe I was logged in as root and added a utility to my /tmp directory, which the mythtv user doesn't have permission to.

So my problem is that when I rebooted, I get an error when starting an xsession saying no permission to access /tmp directory. This occurs just after mythbackend is loaded and while the GUI is being loaded (KDE and then mythfrontend). Chances are, I loaded a program that runs on boot that is located in the /tmp directory. And since mythtv user doesn't have access to this root directory, it throws the error.

I am not looking for help to debug this exact issue, since it is too vague to describe well here. But rather I am interested in ways I can debug ANY general boot issues in knoppix. Specifically:

1. What can I use to get to a prompt so I can debug the start up script for my machine? I was thinking either loading a knoppix boot disk, or SSHing in since mythbackend was running upon the error. Or is there a command to break out of the boot sequence to a prompt?

2. Where are the key start up scripts in Knoppix / Knoppmyth where I can see whats being loaded during bootup? (I am new to Linux, and far too used to a standard DOS autoexec.bat script hah).

Any general debian/knoppix/linux related tips are greatly appreciated since this is a learning experience for me.
Author:  slowtolearn [ Fri Jun 29, 2007 12:17 pm ]
Post subject:  Re: Can't boot due to permissions error
tzoom84 wrote:
I've successfully been able to install KnoppMyth and starting adding and configuring some additional utilities for fun.

Unfortunately, I believe I was logged in as root and added a utility to my /tmp directory, which the mythtv user doesn't have permission to.

So my problem is that when I rebooted, I get an error when starting an xsession saying no permission to access /tmp directory. This occurs just after mythbackend is loaded and while the GUI is being loaded (KDE and then mythfrontend). Chances are, I loaded a program that runs on boot that is located in the /tmp directory. And since mythtv user doesn't have access to this root directory, it throws the error.
As with any software troubleshooting, specific error messages will go a long way in getting others to help :wink:

tzoom84 wrote:
I am not looking for help to debug this exact issue, since it is too vague to describe well here. But rather I am interested in ways I can debug ANY general boot issues in knoppix. Specifically:

1. What can I use to get to a prompt so I can debug the start up script for my machine? I was thinking either loading a knoppix boot disk, or SSHing in since mythbackend was running upon the error. Or is there a command to break out of the boot sequence to a prompt?
Is X starting? In other words, are you getting to the screen with Tux watching TV? If so, you can bring up an Xterm window with Alt-X. If not, I'm not sure what to tell you as I would have guessed you would be at a test login prompt. Another way to get a login prompt from the GUI would be ctrl-alt-f1.

tzoom84 wrote:
2. Where are the key start up scripts in Knoppix / Knoppmyth where I can see whats being loaded during bootup? (I am new to Linux, and far too used to a standard DOS autoexec.bat script hah).

Any general debian/knoppix/linux related tips are greatly appreciated since this is a learning experience for me.
The log files are the first things to check, they reside in /var/log. Also see http://www.knoppmythwiki.org/index.php?page=LinuxTips The Wiki is a very valuable resource.
Author:  tzoom84 [ Fri Jun 29, 2007 3:02 pm ]
Post subject: 
Thanks for the quick reply! Yeah my intent with the question wasn't as much to get that exact error fixed. But rather, what to do with any general linux/knoppix boot-related problem.... plus I was at work at the time of posting and didn't have the exact error msg at hand. :)

I was a bit overwhelmed with all the boot-related config files with linux so I was looking for I guess a sequence of events for what Knoppix/Knoppmyth does when I press that power button. (What key config files are called, etc) I couldn't find this in the general linux tips in the wiki

Later today I'll definately try the alt-x to get to a login prompt. And I'll provide details of the error/solution later on. :) Although I am certain it is from my stupidity of installing a program in the root directory that boots on startup. :)
Thanks.

(Side Note: As for the error, I am able to get to Tux watching tv. And it loads completely through until the loadbar is complete where the NVidia driver is then loaded, and then the error occurs. I noticed I was able to get to a console that shows the boot output terminal by a 'brute force' method (i.e. pounding all keys until a screen pops up. Unfortunately, I couldn't Ctrl-C or Ctrl-X out of the console to break the boot sequence. )
Author:  slowtolearn [ Fri Jun 29, 2007 4:19 pm ]
Post subject: 
tzoom84 wrote:
I was a bit overwhelmed with all the boot-related config files with linux so I was looking for I guess a sequence of events for what Knoppix/Knoppmyth does when I press that power button. (What key config files are called, etc) I couldn't find this in the general linux tips in the wiki
The beginning portion of the bootup is the kernel loading (plus modules), and the user-configurable stuff that happens during boot is found within the /etc/rcX.d directories, where X is 1 - 5. If you installed something and it is starting during boot, most likely the startup script will be in one of those directories (but, as you didn't mention what you installed, that is purely a guess)

tzoom84 wrote:
Later today I'll definately try the alt-x to get to a login prompt. And I'll provide details of the error/solution later on. :) Although I am certain it is from my stupidity of installing a program in the root directory that boots on startup. :)
I doubt that installing something in the / or /tmp directories would cause the problem. /tmp is meant to hold temporary files and is cleared during a reboot.

tzoom84 wrote:
(Side Note: As for the error, I am able to get to Tux watching tv. And it loads completely through until the loadbar is complete where the NVidia driver is then loaded, and then the error occurs. I noticed I was able to get to a console that shows the boot output terminal by a 'brute force' method (i.e. pounding all keys until a screen pops up. Unfortunately, I couldn't Ctrl-C or Ctrl-X out of the console to break the boot sequence. )[/size]
Check through the logs in /var/log once you get to a terminal and look for references to whatever you installed.

If you provide more information about what you installed, others may have a "been there, done that" solution for you.
Author:  tzoom84 [ Mon Jul 02, 2007 4:35 pm ]
Post subject:  UPDATE: SOLUTION - final Questions
Better Explanation of Error + Solution Follows
Well I haven't been home all weekend so I finally got a chance to play around with the error this evening. Turns out I never got to the Tux screen. Actually, I never did see the Tux since my last install because I am running KDE rather than the default Knoppmyth GUI.

So now that I had access to the machine, the exact error is:
"Xsession: warning: unable to write to /tmp; X session may exit with an error"

The error occurred after mythbackend is loaded, and as KDE begins to load. And the most recently installed apps were ddclient to auto-update my dynDNS and Nestopia for NES emulation. Both were unpacked from the /tmp directory.

Googling for this error brought me to linuxquestions.org. The proposed solution there was that the error is caused by the /tmp folder being full, and that running "sudo apt-get update". I did that and it worked like a charm! Turned out after checking with the du command, I only have ~2% free space on my Knoppix partition (that is 10G).

Update: The reason for the ~2% left in the linux partition is that my /home/mythtv/.xsession-errors file was 6.1 GB! So I cleaned it out but now just curious why that was so huge over just a week.
Author:  tzoom84 [ Mon Jul 02, 2007 4:47 pm ]
Post subject: 
So although I have it cleared up for now, I'd still like to know a bit more about apt-get and general stuff to see what went wrong:

A few questions if you all dont mind :)

1. I've only had KnoppMyth installed (on a clean drive) for a week. How do you think /tmp, or the drive in general, was already full? I was using apt-get update often. Does it have to do with that? And what exactly does apt-get clean do?

2. Should I run apt-get clean often to make sure this doesn't occur again? Or are there other ways to prevent it?

3. I've been unpacking/compiling from my /tmp directory to install apps. Is there a better place to unpack apps? I assume that once I make/install in the /tmp directory, it operates from there until I 'uninstall' it. Is that generally correct?
Author:  slowtolearn [ Mon Jul 02, 2007 5:58 pm ]
Post subject: 
tzoom84 wrote:
1. I've only had KnoppMyth installed (on a clean drive) for a week. How do you think /tmp, or the drive in general, was already full? I was using apt-get update often. Does it have to do with that? And what exactly does apt-get clean do?
From man apt-get;
Quote:
clean clean clears out the local repository of retrieved package
files. It removes everything but the lock file from
/var/cache/apt/archives/ and /var/cache/apt/archives/partial/.
When APT is used as a dselect method, clean is run automati-
cally. Those who do not use dselect will likely want to run
apt-get clean from time to time to free up disk space.


tzoom84 wrote:
2. Should I run apt-get clean often to make sure this doesn't occur again? Or are there other ways to prevent it?
You need to be very careful when running apt-get. You can hose your system pretty quickly as many of the dependencies involved with <insert application here> can toast the existing workings of KnoppMyth. Keep in mind that KnoppMyth was put together to be an appliance, or serve a single purpose (that would be to act as a PVR/media distribution unit), and not as a general-purpose desktop distribution. If you are after the latter, you may want to check out Knoppix, [K,X]Ubuntu or the like.

tzoom84 wrote:
3. I've been unpacking/compiling from my /tmp directory to install apps. Is there a better place to unpack apps? I assume that once I make/install in the /tmp directory, it operates from there until I 'uninstall' it. Is that generally correct?
Depending on the application you may need to give the ./configure some options. Check the README that comes with the app. The options can vary greatly, including but not limited to the installation path.
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