Ignore Rust's target build directories in Deja-Dup

I use Deja-Dup, to backup my Ubuntu machines. And just like shimo describes in this blog post, I too want to avoid backing up gigabytes of node_module directories¹.

But I also want to avoid backup up gigabytes of target directories from building Rust projects with Cargo. I have accumulated some 50+ Rust codebases scattered throughout my project directories. Their combined target directories take up about 9GB at time of writing. And all of that is reproducible, cache-like data. It doesn’t need to be backed up.

So, I adapted Shimo’s crontab to add .deja-dup-ignore to all:

• All directories named target
• Where the parent directory has a Cargo.toml file

In a crontab:

05 10    *   *   *   find ~/ -type d -name target -exec bash -c 'if [ -f "$(dirname {})/Cargo.toml" ]; then touch "{}/.deja-dup-ignore"; fi' \; 2>&1

The command runs find, which will execute a bash command on every directory called target. This bash command then gets for the parent dir - $(dirname {}) - of this target directory. It will then check if this parent dir has a Cargo.toml file - if [ -f "$(dirname {})/Cargo.toml" ]; and if so, add a .deja-dup-ignore ignore file in this target dir.

I don’t just want to ignore any target directory. I have at least one legit directory named target (containing a business target). There will be more, there probably are already. Hence the added check for the Cargo.toml file.

This speeds up my backup from over an hour a week, to under 20 minutes a week. And it saves me some 20GB in backup space. Almost a quarter of the space of my incremental backups were node_modules and target directories.