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I recently saw this blog post regarding performance when the TZ environment variable is not set: https://blog.packagecloud.io/eng/2017/02/21/set-environment-variable-save-thousands-of-system-calls/

I have noticed this problem when stracing running daemons on my systems and would like to fix it. I reviewed the official Ubuntu documentation for where to define environment variables: https://help.ubuntu.com/community/EnvironmentVariables

I tried defining TZ in /etc/environment and in /etc/profile.d/test.sh, but I cannot get this environment variable to be available in all cases (e.g. if I just execute bash without --login or if I run the sample c program provided in the above article). How can I make the TZ environment variable defined completely system-wide?

Thanks!

Edit: It was suggested that my question is a duplicate of this other post, but the methods described in that post do not solve this problem. I tried both of these: sudo dpkg-reconfigure tzdata and sudo timedatectl set-timezone America/New_York. After, I confirmed that /etc/localtime is a valid symlink as expected. However, after a reboot I still see 10 stat() calls to /etc/localtime as documented in the original article I posted above. The behavior I am looking for (as documented in the original article) is making it so /etc/localtime is not stat()-ed repeatedly, which is very inefficient

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    Did you log out (of the desktop session) and back in after modifying /etc/environment or /etc/profile.d/xxx? AFAIK those changes should propagate down from the shell that's started by the display manager
    – steeldriver
    Mar 28, 2017 at 16:22
  • Yes, I rebooted. Note that I want this variable to be available from services started via upstart or systemd, which could execute with /bin/sh or another shell (not bash) and thus may not read in /etc/profile.d/*
    – Andrew Martin
    Mar 28, 2017 at 17:03
  • I'm only scratching the surface with systemd, but as far as I can make out your options are to specify EnvironmentFile=-/etc/environment in your unit files, or set a DefaultEnvironment="TZ=whatever" as specified in the systemd-system.conf manpage (I don't think there is currently a DefaultEnvironmentFile)
    – steeldriver
    Mar 28, 2017 at 17:58
  • That is not how you set your TZ, see askubuntu.com/questions/323131/setting-timezone-from-terminal
    – Panther
    Mar 28, 2017 at 18:07
  • 3
    Possible duplicate of setting timezone from terminal
    – Panther
    Mar 28, 2017 at 18:07

1 Answer 1

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I assume you did something like

TZ=:/etc/localtime

This will not however propagate to subshells - and you normal bash shell is a subshell of the wider environment. So you need to do:

export TZ=:/etc/localtime
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  • Correct. Neither of these worked, even after a reboot. I need a solution that will work for upstart jobs and systemd units as well as commands invoked via other shells (e.g. sh, dash, ash, etc).
    – Andrew Martin
    Mar 28, 2017 at 17:03
  • @AndrewMartin most of those start with clean environments, and usually don't have any common file for setting an environment.
    – muru
    Apr 3, 2017 at 5:21
  • Thanks, it sounds like I will need a multi-faceted solution then.
    – Andrew Martin
    Apr 5, 2017 at 16:59

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