"Variables set by the user must have a name consisting solely of alphabet‐ ics, numerics, and underscores - the first of which must not be numeric." - dash.1 it seems the initramfs-tools manpage added the "dash" along the lines, which is wrong for this cornercase of /tmp noexec and no busybox. Then scripts are unfortunately variable names and thus should not have dash in their names. -- maks