Re: [gentoo-user] Performing a backup during the boot sequence

[Allan Gottlieb <gottlieb@nyu.edu>]

At Wed, 26 May 2010 17:17:45 +0200 Daniel Troeder <daniel@admin-box.com> wrote:

> On 05/26/2010 12:30 AM, Allan Gottlieb wrote:
>> For quite a while I have used the following steps to perform a
>> "single-user backup"
>> 
>> 1.  Boot to single user mode via the grub command
>>         kernel /boot/vmlinuz root=/dev/sda6 single
>> 
>> 2.  Type in the root password.
>> 
>> 3.  Execute a single command
>>        /usr/local/sbin/ajg-backup-init-3
>>     which does the backup and then executes
>>        init 3
>> 
>> 4.  This gets me to multi-user mode.
>> 
>> I would like to automate this so that booting directly to multi-user
>> mode via
>>         kernel /boot/vmlinuz root=/dev/sda6
>> 
>> All I need to do is to execute the single command
>>        /usr/local/sbin/ajg-backup-init-3
>> at the right moment.
>> This didn't seem hard; I want it after everything in boot but before
>> everything currently in default.  So I was going to put it in
>> default with a "before *" in depend()
>> 
>> Reading the gentoo handbook chapter B4.d "Writing Init Scripts"
>> I find two comments criticizing this approach
>> 
>> 1.  "You can also use the "*" glob [argument to before] to catch all
>>     services in the same runlevel, although this isn't advisable".
>> 
>> 2.  "Note: Make sure that --exec actually calls a service and not just a
>>     shell script that launches services and exits -- that's what the
>>     init script is supposed to do."
>> 
>> I can see problems with multiple "before *" directives, but no other
>> script has one so I think I would be OK with my "before *".
>> 
>> Criticism 2 has me concerned since my backup routing is indeed a shell
>> script that exits.  Indeed, my backup is not really a service so I am
>> worried that I shouldn't be using an initscript at all.
>> 
>> Any advice/comments would be welcome.
>> 
> You could create a LVM-snapshot of the partition/data you wish to backup
> at "before *" or inside "boot" and then later run the backup on the
> mounted snapshot, removing it afterwards.

Thanks, but I am not trying to minimize the boot time.  The disk to disk
dumps are fast enough (I do the slower copy to a remote site after
logged in).  I am just trying to have the dump done at the right point
in the boot sequence without manually going into single user mode.  If I
could automate the snapshot, I could automate the dump.

Indeed rereading the gentoo manual, I see that the requirement that you
invoke a service and not a script that exits, applies only to
start-stop-daemon, so I will just try to invoke my script directly from
the init script.

allan