utmps

• Solves 32bit time_t problem; however, all applications need to be reviewed for 64bit time_t

• w will not work in future versions of shadow due to login not recording any utmp entries: https://github.com/shadow-maint/shadow/issues/945

• Either link or preload using LD_PRELOAD=libutmps

• We can rely on musl’s utmp.h (after patching) and only remove its utmpx.h

• lh-bootstrap also has instructions on how to improve linking to utmps and skarnet (try it for toybox)

skarnet: “All in all, I believe the flexibility it offers overweighs the inconvenience of having to run services before providing utmp/wtmp.”

utmps is a solution to systems using s6, and won’t work for systemd, and it implements utmpx safely using a daemon

• https://www.thkukuk.de/blog/Y2038_glibc_utmp_64bit/
• https://www.thkukuk.de/blog/Y2038_glibc_wtmp_64bit/
• https://www.thkukuk.de/blog/Y2038_glibc_lastlog_64bit/
• https://github.com/thkukuk/lastlog2
• https://github.com/thkukuk/wtmpdb
• https://github.com/thkukuk/utmpx/blob/main/Y2038.md
• https://www.reddit.com/r/voidlinux/comments/g2wyon/musl_people_how_do_you_do_user_accounting_without/
• https://unix.stackexchange.com/questions/567012/how-can-i-add-lastlog-support-to-alpine-linux
• https://github.com/util-linux/util-linux/issues/2088
• https://wiki.musl-libc.org/roadmap.html
• https://en.wikipedia.org/wiki/Utmp

• utmp.h has been deprecated in 2001 in favor of utmpx.h

• On Glibc systems the former utmp.h is just an alias (or a symlink) for the latter utmpx.h

• On musl libc, utmps can be used to provide utmpx functionality - but not utmp (This means that applications like procps-ng either don’t work properly (w shows nothing under musl with default no-op implementation), or fails to build (utmps provides utmpx.h but no utmp.h)

• utmps also uses a daemon as the only authority to manage the utmp and wtmp data, which is an extra service to consider

• we also need to remove the stub header utmpx.h (and maybe even utmp.h) provided by musl if you plan on using skarnet’s utmps

• we also need to patch multiple software to support utmpx.h instead of utmp.h since utmps only provides the latter. Here’s a list of packages using utmp h (that might require patching) that I compiled based on my experiments in glaucus:

  • autoconf
  • gcc (in libsanitizer)
  • musl
  • procps-ng (for w and whattime)
  • shadow
  • toybox (some pending tools)
  • util-linux (for agetty)

From the musl wiki FAQ:

Q: Why is the utmp/wtmp functionality only implemented as stubs?

• if the feature is implemented, you need to take additional measures to protect your user’s privacy
• in order to use the utmp/wtmp feature, you need a suid/sgid binary to modify the database, which opens the door for security issues:
• if you compromise those binaries, you can inject arbitrary data into the db, that other programs might interpret in exploitable ways
• that’s a HUGE risk to pay for the sake of a basically-useless and possibly-harmful “feature”

The only distribution (other than glaucus) that has a working utmps with s6, musl and other packages is Adélie Linux

For further reading:

• https://gitlab.com/procps-ng/procps/-/merge_requests/67
• https://code.foxkit.us/adelie/packages/blob/master/system/procps/use-utmpx.patch
• https://irclogs.alpinelinux.org/%23alpine-linux-2019-03.log

https://github.com/dslm4515/Musl-LFS/issues/33

• w, getty, tmux, libutempter, shadow, util-linux, procps-ng all use utmp/utmpx (For utmps)

DEPRECATE UTMP, UTMPX, UTMPS, WTMP, BTMP AND LASTLOG

• https://github.com/glaucuslinux/cerata/commit/2173b4c9944027ba69dc5b31b22b6955307c112a
• https://www.tenable.com/audits/items/CIS_Ubuntu_12.04_LTS_Server_v1.0.0_L2.audit:aba64ea9780bd411ca0074d3730917d8
• https://github.com/util-linux/util-linux/issues/2088
• https://github.com/thkukuk/utmpx/blob/main/Y2038.md

When these are removed, distros are using systemd journal and logind to replace them: https://gitlab.archlinux.org/archlinux/packaging/packages/procps-ng/-/commit/749fd577af6fe8ca6218822039078a0c75e3d459