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Old 08-21-2005, 09:10 PM   #1
txtedmacs
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Key combinations that will stop a boot?


I have at least two messages indicating what may be important errors that sweep past so swiftly I have been unable to read either completely (it's possible they are duplicates, since I can tell they are very similarly structured).

I have seen hints that on some machines (and distributions (?)) it is possible to stop the linux boot. I should point out that I have done the obvious by grep(ing) on selected words I have read in the messages on just about every log file I have found in /var/log/ without a match. For example, not in: dmesg, syslog, messages and a slew of others. Words used: [Ww]arn.* non-.* (for non-option, varied the case when I tried more extended strings) and a number of other words. Tests on things on expected words and devices showed multiple matches so it is not my limited skill with grep that is the problem.

I have attempted to search this site with most "hits" seemingly unrelated the my search "stopping boot" and I have done no better using Google where the latest began with "Linux" added to "stop boot" for the exact wording. The nearest that got was how to do it on a Windows type distribution, others seemed completely unrelated.

I would even be appreciative for search strings that might yield more pertinent advice.

I am running Debian initially based on Sarge and modified extensively with packages from both Testing and Unstable.

TIA
 
Old 08-22-2005, 09:15 AM   #2
TigerOC
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Don't think this is possible since the process is done on a ram disk via the initrd.img and therefore is out of the control of the user once initiated.
 
Old 08-22-2005, 09:19 AM   #3
theYinYeti
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When the booting process is done, you can always look back on all the messages that were issued in the log files under /var/log.

Yves.
 
Old 08-22-2005, 09:22 AM   #4
oneandoneis2
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You could insert a "sleep" command into the init scripts so you have time to note down the error messages during boot.

And you can scroll through the messages using something like Ctrl-PgUp or something, I forget exactly what. . .
 
Old 08-22-2005, 09:49 AM   #5
txtedmacs
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Quote:
Originally posted by theYinYeti
When the booting process is done, you can always look back on all the messages that were issued in the log files under /var/log.

Yves.
Would you hazard a guess as to which log file might contain the warnings I see fly past? You seem to have missed my saying I searched this location naming the log files and some of the techniques I employed. Nonetheless, nothing having words I know were in the messages could be found either by grep(ing) or manual searches in an editor. If I had not had a complete failure to find these messages by several means I would not have posted this question. Moreover, I even described my attempts to find other published instances using both this site and via Google - after which I asked even for a better search string. Next time please read the message before giving obvious, but erroneous advice.
 
Old 08-22-2005, 10:05 AM   #6
theYinYeti
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Sorry, I was in a bit of a hurry. I think this would be /var/log/messages but I'm not on Linux right now and it seems I can't be of much help...
Good luck!

Yves.
 
Old 08-22-2005, 10:09 AM   #7
TigerOC
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There are no log records for the ram disk phase (kernel drivers). Log records start once the init scripts are initiated.
 
Old 08-22-2005, 02:54 PM   #8
txtedmacs
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Quote:
Originally posted by TigerOC
There are no log records for the ram disk phase (kernel drivers). Log records start once the init scripts are initiated.
You may be correct, however, why am I seeing in both dmesg and syslog the early recognition of devices and their setup that occur much earlier boot process than the warning messages I fail to see recorded anywhere within the many log files I have searched?

While I have found that Ctrl-PgUp is supposed to scroll upward in the terminal mode, my attempts to test it were utter failures. In my Google searches I have seen hints that this does not work with the 2.6.x kernel I am running.

Another suggestion made earlier about putting sleep into one of the init scripts is of interest, but I am having problems locating the proper stream of booting scripts. Those I have looked at seemed to be devoted to shutting down the process when there is some critical failure.

Could anyone tell me (on a Debian system) where I should begin, i.e. the exact name and location of the init script? I would even just settle for the proper name!

Again TIA to all that have offered suggestions.
 
Old 08-22-2005, 03:00 PM   #9
zedmelon
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Quote:
Originally posted by oneandoneis2
you can scroll through the messages using something like Ctrl-PgUp or something, I forget exactly what. . .
Shift-PgUp and Shift-PgDn will scroll up and down a few screens' worth of SO.

[edit: oneandoneis2 was dead-on correct.
I just discovered Secure CRT (at least version 4.2) will scroll up one line at a time with CTRL-PgUp. The above works directly at a terminal console on many Linuxes/UNIXes, half a screen at a time. Obviously, sCRT won't give your boot readout, but connectorizin' from a Winderz box with no mouse just became easier ;)
]

Last edited by zedmelon; 08-28-2005 at 03:57 PM.
 
Old 08-22-2005, 04:16 PM   #10
makuyl
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Hit "scroll lock" when you see the message. If it went already, use shift-pageup
 
Old 08-22-2005, 06:24 PM   #11
txtedmacs
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Quote:
Originally posted by zedmelon
Shift-PgUp and Shift-PgDn will scroll up and down a few screens' worth of SO.
THANKS!!! Worked like a charm - would have replied earlier, but changing out some memory and a new, larger hard drive to run a second distribution of Linux. Never had Windows on this machine.

The shift-PgUp worked as a test on the shutdown to reboot, and landing in the login due to running a safe boot the shift-(many)PgUp got me to the messages. As suspected the warning was a duplicate. The particular problem was known to me (find command), but not its solution. I will post that under a separate thread later, since it's apparent failure writing to a file in the /proc directory.

Thanks again to everyone for the help, I am quite surprised it works so easily without disruption of the boot. After looking at the messages at my leisure the Ctrl-D took me fully into Linux as a user without a hitch.
 
Old 08-22-2005, 08:03 PM   #12
eqxro
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If you use grub as bootloader, you can edit the kernel parameters by pressing "e" on the required entries. You can stop the init by simply setting root=/somethin_fake on this entry. This would load the kernel and bomb when it would try to mount the root partition (which obviously does not exist). This can provide you with even a shell prompt. To boot normally you must either specify the root partition or manually mount, or simply reboot. It's ugly, but does the trick

Last edited by eqxro; 08-22-2005 at 08:04 PM.
 
  


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