Charly's Column – systemd-analyze

If a distribution shows its splash screen on startup – and almost all of them do – then I turn it off as of the second boot. I want to see the kernel messages rushing by when booting. Because more often than you might think, there's a problem with booting. When I see something questionable scurry by, I search with a tool like Bootchart [1] to find and fix a hanging process or similar issues quickly.

On systems with systemd, this is also possible in principle, but the tool is different: systemd-analyze. When called without parameters, systemd-analyze calculates the elapsed time until system startup is completed, broken down into kernel and userspace processes:

Startup finished in 3.507s (kernel) + 16.334s (userspace) = 19.842s

Of course, I want to know more about those processes now. The command systemd-analyze blame gives me a list of all processes started at boot time. They are sorted by the elapsed time before the process has fully launched. I usually only see the 10 biggest time hogs, as shown in Listing 1.

1min 3.753s apt-daily.service
    40.702s apt-daily-upgrade.service
     8.649s fail2ban.service
     4.246s networking.service
     3.327s smokeping.service
     2.622s apache2.service
     2.303s mysql.service
     2.206s postfix.service
     1.835s dev-sdb1.device
      993ms munin-node.service

In this particular case, I can ignore the candidates in lines 1 and 2 – they appear if the system performs unattended updates or upgrades on startup. Fortunately, they do not block any other processes and simply wriggle around a bit in the background. systemd-analyze does not calculate them for this reason, as can already be seen from the sums.

Serial Plot

With the plot parameter, I can create a kind of timeline in SVG format, which shows the boot process in a very clear graphical way. For this to work, the graphwiz package must be installed. The command is then:

systemd-analyze plot > systemd-boot.svg

Figure 1 shows a small section of the results. The start time of the individual processes is symbolized here by a red bar. Not only the start order and times, but all the dependencies between the services, can be summarized by the tool in the form of an SVG graphic:

systemd-analyze dot | dot -Tsvg > dependencies.svg

Figure 1: An SVG format timeline showing each service's system start times.

Caution: The result is really huge and probably only makes life easier for owners of A1-sized plotters.