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Re: An experiment in backup



On Thu, Jan 15, 2015 at 07:19:52PM -0800, Kevin O'Gorman wrote:
>    I'm trying to develop a reliable backup method that does not use
>    proprietary tools or formats, and is free as in beer.  I thought I had it,
>    but i just tried a restore, and it's a miserable failure.  I wonder if
>    anyone here can point out the error of my ways.
> 
>    I have a tar backup of the entire system, excluding /sys, /proc and /dev.
>    I have a tar backup of a bind-mount of /dev.

Skip these.

/sys and /proc are "pseudo-filesystems" in that they are representations
of kernel settings in a file system format. Some of these "files" are
read only (for example the contents of /proc/net/dev are statistics on
all your network devices; in this case, it makes no sense for userspace
to be telling the kernel how many packets have been recieved, so you
can't write to the file), some of the files are write only (for example
/proc/sysrq-trigger which can be used to simulate pressing
SysRq+<something>). And besides, neither of these filesystems is
persistent (the contents are lost at shutdown and recreated when the
filesystem is mounted).

/dev, similarly, is (since the days of devfs) a dymanic filesystem
containing only communication end-points to your devices. You could back
up the device nodes, but because the kernel autodiscovers hardware and
creates the devices nodes at boot, you'll either have exactly the same
thing (if the autodetection happened in exactly the same manner) or the
WRONG device nodes.


>    These were taken while the system was running, but quiet.  I did it this
>    way because I cannot get the system to boot into single user mode. 
>    Putting "single" on the end of the "linux" like results in a black screen.
> 
>    I restored these, created /sys and /proc, and tried to boot the resulting
>    partition.  It boots, but X does not come up, or even seem to try.  I can
>    do a console login to my usual account, and stuff is there.
> 
>    I'm quite clueless as to why this is happening.  I could sure use some
>    help.
>    --
>    Kevin O'Gorman
>    #define QUESTION ((bb) || (!bb))   /* Shakespeare */
> 
>        Please consider the environment before printing this email.


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