Remove what remains of the overlayfs support, `--overlay` commands and
the `--enable-overlayfs` configure option.
Commands:
* `--overlay`
* `--overlay-named=`
* `--overlay-clean`
* `--overlay-tmpfs`
firejail.config:
* `overlayfs`
Related commits:
* 489cc25c2 ("cleaned up old overlayfs code; the feature was disabled by
default in 2021 because of security problems", 2025-12-16).
* b537aa57b ("fixed /sys mounting broken during overlayfs cleanup",
2025-12-18)
Relates to #6994.
Note: Code with `RUN_OVERLAY_ROOT` / `oroot` is left as is, since it
seems to also be used by `--chroot`:
$ git grep -E '[^n]oroot'
etc/apparmor/firejail-default:# Line starting with /run/firejail/mnt/oroot deal with --overlay sandboxes.
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{dev,etc,home,media,mnt,root,srv,tmp,var}/** w,
etc/apparmor/firejail-default:# to run programs from your home directory, add "/{,run/firejail/mnt/oroot/}home/** ix,"
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{,usr/,usr/local/}bin/** ix,
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{,usr/,usr/local/}sbin/** ix,
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{,usr/,usr/local/}games/** ix,
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{,usr/,usr/local/}lib{,32,64,exec}/** ix,
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{,usr/,usr/local/}opt/** ix,
etc/apparmor/firejail-default:#/{,run/firejail/mnt/oroot/}home/** ix,
etc/apparmor/firejail-default:/{,run/firejail/mnt/oroot/}{,var/}run/firejail/appimage/** ix,
src/firejail/chroot.c: // create /run/firejail/mnt/oroot
src/firejail/chroot.c: char *oroot = RUN_OVERLAY_ROOT;
src/firejail/chroot.c: if (mkdir(oroot, 0755) == -1)
src/firejail/chroot.c: // mount the chroot dir on top of /run/firejail/mnt/oroot in order to reuse the apparmor rules for overlay
src/firejail/chroot.c: if (bind_mount_fd_to_path(parentfd, oroot))
src/firejail/chroot.c: errExit("mounting rootdir oroot");
src/firejail/chroot.c: if (chroot(oroot) < 0)
src/include/rundefs.h:#define RUN_OVERLAY_ROOT RUN_MNT_DIR "/oroot"
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