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Top Forums UNIX for Advanced & Expert Users Why is editing a file by renaming the new one safer? Post 303042601 by vbe on Wednesday 1st of January 2020 04:00:35 AM
Old 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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savecore(1M)                                              System Administration Commands                                              savecore(1M)

NAME
savecore - save a crash dump of the operating system SYNOPSIS
/usr/bin/savecore [-Lvd] [-f dumpfile] [directory] DESCRIPTION
The savecore utility saves a crash dump of the kernel (assuming that one was made) and writes a reboot message in the shutdown log. It is invoked by the dumpadm service each time the system boots. savecore saves the crash dump data in the file directory/vmcore.n and the kernel's namelist in directory/unix.n. The trailing .n in the pathnames is replaced by a number which grows every time savecore is run in that directory. Before writing out a crash dump, savecore reads a number from the file directory/minfree. This is the minimum number of kilobytes that must remain free on the file system containing directory. If after saving the crash dump the file system containing directory would have less free space the number of kilobytes specified in minfree, the crash dump is not saved. if the minfree file does not exist, savecore assumes a minfree value of 1 megabyte. The savecore utility also logs a reboot message using facility LOG_AUTH (see syslog(3C)). If the system crashed as a result of a panic, savecore logs the panic string too. OPTIONS
The following options are supported: -d Disregard dump header valid flag. Force savecore to attempt to save a crash dump even if the header information stored on the dump device indicates the dump has already been saved. -f dumpfile Attempt to save a crash dump from the specified file instead of from the system's current dump device. This option may be useful if the information stored on the dump device has been copied to an on-disk file by means of the dd(1M) command. -L Save a crash dump of the live running Solaris system, without actually rebooting or altering the system in any way. This option forces savecore to save a live snapshot of the system to the dump device, and then immediately to retrieve the data and to write it out to a new set of crash dump files in the specified directory. Live system crash dumps can only be per- formed if you have configured your system to have a dedicated dump device using dumpadm(1M). savecore -L does not suspend the system, so the contents of memory continue to change while the dump is saved. This means that live crash dumps are not fully self-consistent. -v Verbose. Enables verbose error messages from savecore. OPERANDS
The following operands are supported: directory Save the crash dump files to the specified directory. If directory is not specified, savecore saves the crash dump files to the default savecore directory, configured by dumpadm(1M). FILES
directory/vmcore.n directory/unix.n directory/bounds directory/minfree /var/crash/'uname -n' default crash dump directory ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
adb(1), mdb(1), svcs(1), dd(1M), dumpadm(1M), svcadm(1M), syslog(3C), attributes(5), smf(5) NOTES
The system crash dump service is managed by the service management facility, smf(5), under the service identifier: svc:/system/dumpadm:default Administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed using svcadm(1M). The ser- vice's status can be queried using the svcs(1) command. If the dump device is also being used as a swap device, you must run savecore very soon after booting, before the swap space containing the crash dump is overwritten by programs currently running. SunOS 5.10 25 Sep 2004 savecore(1M)
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