01-01-2020
I agree also,
I did lose files after crashes but in the early 90s on HP-UX 8, or Linux 0.99... can't remember after with JFS...
As Neo mentions, its not the OS crash the vulnerability but more the Human intervention on those files been modified e.g I saw Sun servers after a reboot where no one could connect, because someone modified the passwd file NOT using vi... and many more similar cases, so for peace of mind I always make a copy I modify and once done add .ori to the original so whatever I can compare... My remarks apply mostly to any Unix configuration files except sudoers need editing with vi ( as depending on the state of the machine is the only editor working...)
It is true that modern editors as Neo described have funky functionalities that are more than simple cosmetics and would be a pity not to use, but also as he adds: with caution..
What I wanted to mention was more: In a panic mode you tend to forget a lot of things like when a system crashes, you may well have a mail ( but who looks at his mbox?) from the system saying you were editing a file and the system saved the state of the file under the name XXXXXXX, you open them with vi -rdepending the content and how bad the crash you may find the system managed to leave the original in his precedent state ( so before editing or last save ) and have in XXXXXX the last state of current modifications of the file, it may not be complete but at least you haven't lost all, and most important it avoided your system some unwanted file corruption... this may be the reason of with JFS no one can remember losing anything these last 25 years...
But it's not a reason for not being careful when doing sysadmin tasks
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LEARN ABOUT FREEBSD
crash
CRASH(8) BSD System Manager's Manual CRASH(8)
NAME
crash -- FreeBSD system failures
DESCRIPTION
This section explains a bit about system crashes and (very briefly) how to analyze crash dumps.
When the system crashes voluntarily it prints a message of the form
panic: why i gave up the ghost
on the console, and if dumps have been enabled (see dumpon(8)), takes a dump on a mass storage peripheral, and then invokes an automatic
reboot procedure as described in reboot(8). Unless some unexpected inconsistency is encountered in the state of the file systems due to
hardware or software failure, the system will then resume multi-user operations.
The system has a large number of internal consistency checks; if one of these fails, then it will panic with a very short message indicating
which one failed. In many instances, this will be the name of the routine which detected the error, or a two-word description of the incon-
sistency. A full understanding of most panic messages requires perusal of the source code for the system.
The most common cause of system failures is hardware failure, which can reflect itself in different ways. Here are the messages which are
most likely, with some hints as to causes. Left unstated in all cases is the possibility that hardware or software error produced the mes-
sage in some unexpected way.
cannot mount root This panic message results from a failure to mount the root file system during the bootstrap process. Either the root
file system has been corrupted, or the system is attempting to use the wrong device as root file system. Usually, an alternate copy of the
system binary or an alternate root file system can be used to bring up the system to investigate. Most often this is done by the use of the
boot floppy you used to install the system, and then using the ``fixit'' floppy.
init: not found This is not a panic message, as reboots are likely to be futile. Late in the bootstrap procedure, the system was unable to
locate and execute the initialization process, init(8). The root file system is incorrect or has been corrupted, or the mode or type of
/sbin/init forbids execution or is totally missing.
ffs_realloccg: bad optim
ffs_valloc: dup alloc
ffs_alloccgblk: cyl groups corrupted
ffs_alloccg: map corrupted
blkfree: freeing free block
blkfree: freeing free frag
ifree: freeing free inode These panic messages are among those that may be produced when file system inconsistencies are detected. The
problem generally results from a failure to repair damaged file systems after a crash, hardware failures, or other condition that should not
normally occur. A file system check will normally correct the problem.
timeout table full This really should not be a panic, but until the data structure involved is made to be extensible, running out of entries
causes a crash. If this happens, make the timeout table bigger.
init died (signal #, exit #) The system initialization process has exited with the specified signal number and exit code. This is bad news,
as no new users will then be able to log in. Rebooting is the only fix, so the system just does it right away.
That completes the list of panic types you are likely to see.
If the system has been configured to take crash dumps (see dumpon(8)), then when it crashes it will write (or at least attempt to write) an
image of memory into the back end of the dump device, usually the same as the primary swap area. After the system is rebooted, the program
savecore(8) runs and preserves a copy of this core image and the current system in a specified directory for later perusal. See savecore(8)
for details.
To analyze a dump you should begin by running kgdb(1) on the system load image and core dump. If the core image is the result of a panic,
the panic message is printed. For more details consult the chapter on kernel debugging in the FreeBSD Developers' Handbook
(http://www.freebsd.org/doc/en/books/developers-handbook/).
SEE ALSO
kgdb(1), dumpon(8), reboot(8), savecore(8)
HISTORY
The crash manual page first appeared in FreeBSD 2.2.
BSD
July 23, 2011 BSD