GNU vs BusyBox Unix tools

Alpine uses BusyBox while Ubuntu uses GNU tools, and they behave differently.

  1. Intro
  2. Exit with code 1
  3. List

Intro §

Skip to the list.

Alpine Linux is known for its minimal size. The ‘mini root filesystem‘ flavour is only 2MB. This size makes it suitable as a Docker image, so CI job can start running script sooner instead of downloading larger image like Ubuntu.

I use it in my urlhaus-filter repo to run the scripts (that update the filter twice a day). When I first started using it on gitlab ci (I only knew about it a week ago), my first impression was that it somehow ships with more Unix tools than Ubuntu (not technically correct which I explain later), despite its minimal size. during the setup of the repo, there were many job failure due to incorrect command options or syntax.

Exit with code 1 §

While setting up GitLab CI for urlhaus-filter, I encountered many issues despite tested fine on my workstation. Sifting through the error messages, I noticed the Alpine’s Unix tools behave differently than mine. I investigated further by testing the script on an Alpine VM.

I compared the --version of those tools in Ubuntu and Alpine, and noticed the outputs are totally different. The Alpine tools output BusyBox vXX, which shows they are part of BusyBox. I briefly read up the wiki and noticed the following line,

…compared GNU, BusyBox, asmutils and Perl implementations of the standard Unix commands…

and the examples,

Programs included in BusyBox can be run simply by adding their name as an argument to the BusyBox executable:

/bin/busybox ls

…, for example just


after /bin/ls is linked to /bin/busybox

So, Alpine uses BusyBox and Ubuntu uses GNU. Ubuntu does include BusyBox by default, but it mostly uses GNU.

List §

I tested the tools on Alpine and Ubuntu, and noted their behaviour. BusyBox = BB.

  • gzip/gunzip/zcat: BB only support gzip/bzip2/xz format, use BB’s unzip for zip file. GNU can only extract the first file in a zip.
  • unzip: GNU doesn’t support stdin as input. funzip can decompress from stdin, but only the first file (like zcat). BB support stdin and extract all files, through unzip -.
  • sed: BB doesn’t support -z argument which is used to find/replace \n new line character. A workaround is sed ':a;N;$!ba;s/\n/<new character>/g' file or sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/<new character>/g' file. GNU sed -z 's/\n/<new character>/g' works.
  • bsdtar: Since GNU can only extract the first file, in addition to BB’s unzip, another alternative is bsdtar. bsdtar is available through libarchive-tools package. To extract zip from stdin, use $ bsdtar -xf -.
  • patch: BB doesn’t support --backup option. BSD doesn’t support --verbose option.