S3E20: "Clockulators"

Comments 0

Previous EpisodeNext Episode
Recorded (UTC) Aired (UTC) Editor
2018-11-24 03:19:43 2018-12-03 03:28:45 "Edita"
Format SHA256 GPG Audio File
MP3 33e344cd7650f3308414ebd45e81e06ae26527710b0519f8ee6edb50ce360c28 click click
OGG 379de39d31f07d9ac1f1272df63cad1579394c91cef78f4cddb000fd50306b01 click click

In this episode, we talk about various timing tools in *nix (at, cron, systemd timers, NTP, etc.)



Starts at 14m07s.

I was drinking another Porterhouse’s An Brain Blásta. Paden was drinking water. Jthan was drinking Coors’ Light (which yes, Jthan, we did have on in S1E13 and S3E0).

  • Time-related tools in *NIX!
    • at
      • Automated one-time execution of commands (scripts, etc.).
      • Useful beginner’s guides can be found here and here, but it’s also in the RUTE and the pink book (see S0E11 notes for links to these).
    • cron(d)
      • You can find a crontab/cronjob parser here, you can find a generator here.
      • The ArchWiki documentation is great.
      • You cannot specify a specific year, Jthan, just how many times a year (down to once a year).
    • anacron
      • Relatedly, anacron is a form of alternate cron that helps you out on machines that are more sporadic with availability. Cronie provides both a crond and anacron interface, but more traditional cronds (such as Paul Vixie’s crond) require a separate or standalone anacron.
    • systemd Timers
      • The Arch wiki is still great, but the upstream docs aren’t too bad either.
      • The challange I posed to Jthan is actually more or less exactly given as an example in the Arch wiki article here.
        • Someone remind me to write a cron to systemd timer converter.
    • NTP
      • NTPv3 is defined in RFC 1305 and NTPv4 is defined in RFC 5905 (proposed).
      • There is a history of security issues related to NTP.
      • Manages a way to bring computers in line with a more reliable timekeeping source (such as NIST’s ytterbium atomic clock), and addressing the tendency to correct the “loose” timekeeping methods consumer timekeeping hardware keeps.
      • VERY important for encryption sessions (handshaking, etc.) and PKI such as X.509!
    • Protip, some DHCP clients, if they support BOOTP, can get their NTP server from DHCP.
      • And in DNSMASQ, you can even reference it by name: dhcp-option=option:ntp-server,, would send the NTP servers and

Sysbadministration Award

In this segment, we highlight system administration mistakes. Think of them as the IT equivalent of the Darwin Awards. (46m20s)

While I love Calibre for my e-reader, the author is nuts. He thinks he can maintain python 2 all by himself (and that it’d be “less work” than converting the codebase).


  • I ignore Jthan at the beginning because no, we never did talk about NTP. We briefly mention OpenNTPD in S0E13, though.
  • I forgot to mention it on-air, but did you know that ESR (author of The Cathedral and the Bazaar) is the project tech lead of a hardened NTP implementation called NTPsec?
  • Jthan does indeed have a shitton of crons:
22:06:08< jthan> root@[redacted]:/root# crontab -l | wc -l 
22:06:09< jthan> 2209
22:13:51< jthan> +
22:13:51< jthan> -bash-4.3$ crontab -l | wc -l 
22:13:51< jthan>     1880


Music Credits
Track Title Artist Link Copyright/License
Intro Whosi sawsquarenoise click CC-BY 4.0
Outro 66666666666666666666 66666666666666666666 66666666666666666666 66666666666666666666 66666666666666666666 66666666666666666666 Monplaisir click CC0 1.0
(All music is royalty-free, properly licensed for use, used under fair use, or public domain.)



There are currently no comments on this article.


Enter your comment below. Fields marked * are required. You must preview your comment before submitting it.