Detecting a chroot jail from within

Question

How can one detect being in a chroot jail without root privileges? Assume a standard BSD or Linux system. The best I came up with was to look at the inode value for \"/\"

Answer 1

On BSD systems (check with uname -a), proc should always be present. Check if the dev/inode pair of /proc/1/exe (use stat on that path, it won't follow the symlink by text but by the underlying hook) matches /sbin/init.

Checking the root for inode #2 is also a good one.

On most other systems, a root user can find out much faster by attempting the fchdir root-breaking trick. If it goes anywhere you are in a chroot jail.