This was fixed in initramfs-tools version 0.123 which is available in Zesty and later releases. The fix should be SRU'ed to both Ubuntu 14.04 and Ubuntu 16.04 which are affected. Here's a link to the commit which fixed this:
https://anonscm.debian.org/cgit/kernel/initramfs- tools.git/commit/?id=ac6d31fc2c707b72ff8af9944c9b4f8af303a6a3 ** Also affects: initramfs-tools (Ubuntu Trusty) Importance: Undecided Status: New ** Also affects: initramfs-tools (Ubuntu Xenial) Importance: Undecided Status: New ** Changed in: initramfs-tools (Ubuntu) Status: Confirmed => Fix Released ** Changed in: initramfs-tools (Ubuntu Trusty) Importance: Undecided => High ** Changed in: initramfs-tools (Ubuntu Xenial) Importance: Undecided => High ** Changed in: initramfs-tools (Ubuntu Trusty) Status: New => Triaged ** Changed in: initramfs-tools (Ubuntu Xenial) Status: New => Triaged -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1713004 Title: Temporary files left under /var/tmp by mkinitramfs To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/initramfs-tools/+bug/1713004/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs