snp: Wrap shell command in BTRFS snapper pre-post snapshots and log outputs.

snp

#!/usr/bin/env bash
# Runs a command wrapped in btrfs snapper pre-post snapshots.
# Usage: $ snp <commands>
# e.g.: $ snp pacman -Syyu
# Requirements: snapper (https://wiki.archlinux.org/title/snapper)
# The latest version of this script is hosted at https://gist.github.com/erikw/5229436

log_path="/var/local/log/snp"
date=$(date "+%Y-%m-%d-%H%M%S")
log_file="${log_path}/snp_${date}.log"

! [ -d $log_path ] && mkdir -p $log_path
# Log stdout and stderr. Reference: http://stackoverflow.com/questions/3173131/redirect-copy-of-stdout-to-log-file-from-within-bash-script-itself
exec >  >(tee -a "$log_file")
exec 2> >(tee -a "$log_file" >&2)

cmd="$@"

echo "> Logging to: ${log_file}"

snapshot_nbr=$(snapper create --type=pre --cleanup-algorithm=number --print-number --description="${cmd}")
echo "> New pre snapshot with number ${snapshot_nbr}."
echo -e "> Running command \"${cmd}\".\n"

eval "$cmd"

snapshot_nbr=$(snapper create --type=post --cleanup-algorithm=number --print-number --pre-number="$snapshot_nbr")
echo -e "\n> New post snapshot with number ${snapshot_nbr}."




# Snapper has a --command option nowadays. But it works worse, the output from the command is not printed separately from the snaptshot number, just becomes a mess.
#echo "> Running command \"${cmd}\"."
#snapshot_nbr=$(snapper create --command "${cmd}" --print-number --cleanup-algorithm=number --description="${cmd}" | tail -1)
#echo -e "\n> New pre-post snapshot with numbers ${snapshot_nbr}."

Hi! Out of curiosity, why did you choose /var/local/log instead /var/log?

Hi msx!

I use the local directory to not confuse my custom files and scripts with the systems. The very same reason people put their own system scripts under /usr/local/{bin,sbin} instead of /usr/{bin,sbin} :)

Just passing by to say TY and let you know that I'm using snp all the time for all sort of things. Cheers!

ZFS users!

Check out znp

=)

Hi,
May I submit a PKGBUILD for this script to the AUR? I believe it will help out a lot of people.

@Fire100265 Hey, you're very welcome to make a PKGBUILD for this! I too find this little utility immensely useful for many semi- to dangerous Linux operational tasks.

I don't know how well PKGBUILDs work with gists. If it's not working out well, I can move this script to a proper Github git repo. Let me know if the Gist works first though

@erikw Thank you! I have written a PKGBUILD and I will be submitting it to the AUR soon. As you have predicted, gists do not work very well with PKGBUILDs. Due to this, I copied all the text into a file and used it as the source.
Edit: Here is the link to the AUR page. Please let me know of any changes I should make. I can add you as a maintainer if you wish.

@Fire100265 The PKGBUILD looks great!

There can only be 1 maintainer in AUR right? To distribute comments and future maintenance questions you could tell people to reach out to me as well of your unavailable, here at Github or my AUR profile https://aur.archlinux.org/account/erikw :)

Thank you for your reply! I added you as a maintainer. Please let me know if you can access the package.
Edit: please edit the PKGBUILD to add your email.

✅

It's been 5 years, but I have to ask this:

Why is this script logging to /var/local/log/snp given that writing to that folder requires root privileges? Is it meant to only be run with sudo?

@cristi-neagu it could be that snapper(1), which is used by snp, requires root privileges? I don't remember.

Fair enough, maybe it did. But it doesn't look like it needs them now. Running snp without sudo creates the pre and post snapshots just fine, but fails to write to log because of folder permissions. Which, to be fair, doesn't stop the script from working, but it is annoying.

Maybe I'm doing something wrong here?

Well, you could just change log_path="/var/local/log/snp" to a path that the user(s)/group(s) you want to run snp with has write permission to. Or change the permission of this directory. There are many ways :)

Using the /var/local/log/ path worked for my use cases, and on the system (Arch) I was on, back then, but it might not for you.

Thanks for the suggestion. Seems like snapper doesn't require root access to create root snapshots on my system for some reason. I can't tell if this is a good thing or a bad thing.