Chroot with a fake root user

This script creates a fake root where your user has write permission to arbitrary locations. It does not require any dependencies.

Why do it?

I wrote this when I had to download and extract a Linux package and run it as a non-root user. Trouble was the package was dynamically loading its shared libraries from /usr/lib64, ignoring the LD_LIBRARY_PATH variable. So the only way I could run it was inside a chroot where I could copy its libraries to the system location. But of course to create a functioning chroot you need to do one of the following things:

• Copy over most directories, such as /etc, /dev and others to the new fake root...

  Not efficient, would take a lot of space and probably fail for /dev, /proc and /sys.

• Mount an overlay filesystem into the fake root

  Ideal solution, except... it requires root

• Bind mount most directories

  Good, but again it requires root... or so I thought!

  Turns out, in some cases you can trick mount into thinking you're root. The article I'm linking to suggests it should work with overlay filesystems, but at least on Amazon Linux it doesn't: it still fails with permission error. However, it works with bind mounts. So I wrote this script.

What it does

It takes a list of directories or files which you want to be writable to your fake root user inside your fake root directory, and bind mounts everything else (for files it creates hard links).

For example if you want a fake root where your fake root user has write access to /usr/bin, /usr/lib64 and /etc/hosts, call the script with:

fake-root-chroot.sh -w /etc/hosts /usr/lib64 /usr/bin -r /path/to/chroot

The script will create the following structure:

/etc -> a new directory owned by the fake root user

/etc/hosts -> a copy of the original /etc/hosts, now owned by the fake root user

/etc/* -> all directories are bind-mounted, all other files are hard-symlinked

/usr/bin -> same as for /etc

/* -> all directories are bind-mounted, all files are hard-symlinked

Any files that are created inside the fake root (i.e. not a hard link to the corresponding file on the real root), will be kept.