First of all, take a copy of your /etc folder. The /etc directory contains all system settings, including your file system table (fstab), Portage-specific settings (/etc/make.conf, /etc/portage), service configuration files (in /etc/conf.d and /etc/env.d), ... Really, this location is not to be forgotten.

Next, there are a few non-/etc files or directories that you want to copy as well.

Next to the system settings, you'll find that your end user(s) on your system also have gone through lots of trouble to set up their system as they want it. End users' configuration settings are stored in the end users' home directories. There is no single directory for all configuration settings, so finding which ones to back up and which not might be difficult. However, one way that works for me (and which usually doesn't include the end users' personal files) is to backup all ${HOME}/.??* files and directories. Most configuration directories (or files) are hidden files (i.e. starting with a period).

The following command will make an archive of the above mentioned settings.

~# tar cvzpf /var/tmp/poormanbackup.tar.gz /etc /var/lib/portage/world /usr/local /proc/config.gz /home/*/.??*

Again, this is just a poor man's backup, because it is not really managed, but it is still better than nothing. Make sure you copy the poormanbackup.tar.gz to a safe(r) place. Note that it will still be fairly large, because of the end user copy (as it contains lots of software caches, like your browsers' cache). If you drop the end user directories (the /home/*/.??*) the file is reduced from many dozens (up to hundreds) of megabytes down to about half a megabyte.

To restore files, get the file on your system (mount the USB stick/CD) and extract the file(s) you need. For instance, to extract all /etc/portage/* files:

~# tar xvzpf /media/usb/poormanbackup.tar.gz -C / etc/portage

Note the space between / and etc/portage!

The backupninja application is a tool which is scheduled to run every night (for instance) and that will read in the configuration file(s) in /etc/backup.d. Inside this directory, you define what needs to be backed up, how often, etc. For instance, the same poor man's backup settings of above would result in a file similar to the following:

File /etc/backup.d/20-basic-system.rdiff to backup regular files:

when = daily
options = --exclude-special-files
nicelevel = 15

[source]
label = myhostname.mydomain
type = local
keep = 60
include = /etc
include = /var/lib/portage/world
include = /usr/local
include = /home/*/.??*
exclude = /home/*/.mozilla/firefox/*.default/Cache

[dest]
type = local
directory = /var/backups/backupninja

File /etc/backup.d/19-kernel-config.sh:

zcat /proc/config.gz > /etc/kernel-config

File /etc/backup.d/21-copy-to-usb.sh:

rsync -avug /var/backups/backupninja /media/usb

The result of this is that the kernel configuration file is generated first (into /etc/kernel-config) after which (incremental) backups are taken of the presented locations, and stored in /var/backups/backupninja. Finally, these files are copied (synchronized) to /media/usb (which might be a USB stick or external disk drive). If you ever want to store that backup outside of your home (for instance, at your parents/kids house), detach the USB stick and store it there. Just make sure another USB stick is attached and mounted for the next backup cycle.

If you installed Gentoo using the sysresccd CD, then you already have the tools at your disposal to perform imaging backups. A popular tool is PartImage, and is available on the sysresccd.

The tool offers a graphical (or curses) based interface, but you don't need to use that: the tool also supports command-line backups.

An example usage would be the following. Boot from the sysresccd, and attach USB storage to your system on which you want to back up your entire system:

~# mount /dev/sdc1 /media/usb

Next, take image(s) of your partitions, or take a full disk backup. Don't worry, PartImage is able to detect when disk space isn't used, and will skip those empty blocks. The following takes a full backup of /dev/sda in blocks of 700Mbyte (in case you ever want to store the files on CD or DVD):

~# partimage -b -z1 -o V700 save /dev/sda /media/usb/gentoo_full.sda.partimg.gz

If you ever need to restore the system, use the following command:

~# partimage -e restore /dev/sda /media/usb/gentoo_full.sda.partimg.gz.000

Specifically for Gentoo, some users have created enhancements on top of the standard "stage3" installation used by Gentoo Linux. With stage4 or stage5 installations, the extracted tarball is a lot larger (it contains almost an entire system) and might be accompanied with additional script(s) that set up or recover the system. These scripts can, for instance, restore your partition layout, reformat the partitions, reinstall the bootloader, etc.

Compared with the poor man's backup approach described above, this can be seen as a "entire system poor man's backup", with optionally

I personally prefer imaging software for such large recovery scenarios. However, such stage4/stage5 installations prove to be useful when you migrate your system from one disk to another. Using imaging tools might fail here, because they often require that the target hard disk is equally sized, whereas you probably want to migrate to a larger disk.

So, if you are interested in a stage4 or stage5 backup/restore, you can take one from a running system or booted from a livecd. I suggest using a livecd (or other live environment) as that will ensure that the restore of the archive will give you a sane situation. If you take such an archive while running inside the system itself, you will also copy state files and other files that should not be there when a system is being booted.

Mount your file systems (say at /mnt/gentoo) except for the dynamically created ones (like proc, dev, sys, ...). Then, run the following tar command to create the archive:

~# tar -cvzpf /media/usb/backup/stage4.tar.gz --numeric-owner --strip-components=2 /mnt/gentoo

The --numeric-owner will ensure that uid/gid numbers are used rather than names, because the live environment can use different name/id pairs than your own system. By using --strip-components=2, all files are stored in the archive without the leading "/mnt/gentoo".

If you need to put back the backup, you can recreate your partitions (or create new ones), mount them somewhere (say /mnt/gentoo again) and run:

~# tar xvzpf /media/usb/backup/stage4.tar.gz -C /mnt/gentoo

Don't forget to reinstall the boot loader before you reboot!