I2'm trying to fully make sense of the boot process with systemd. I've read various pages from the manual, including bootup(7). There are two points I don't fully understand.
* Filesystem mounts during initrd The man page, under the initrd section, says: "systemd detects that it is run within an initrd [...]. The bootup process begins identical to the system manager bootup (see above) until it reaches basic.target. [...] Before any file systems are mounted, it must be determined whether the system will resume from hibernation or proceed with normal boot." In my mind, that part self-contradicts when both saying that 1) the bootup proceeds identical to the system manager bootup and 2) a determination on whether to mount file systems is made /after/ basic.target. This is because some file systems (including, in most cases, the root file systems) would have been mounted before local-fs.target, which is ordered before basic.target. So either the process is not really identical until basic.target, or I'm getting something wrong. * Instances I gather that the systemd which runs inside the initrd is a completely separate instance from the one which then runs in the booted system. Which implies - as discussed above - that the system initialization sequence from beginning to basic.target actually happens twice. Does this means than any initialization units which could potentially be run twice - once in the initrd and once in the booted system - should be instrumented to avoid running their logic twice (in the cases where that's not needed or even harmful)? Let's consider for example an hypothetical service with "WantedBy=cryptsetup-pre.target", which decrypts a keyfile using an hardware token. This keyfile is then consumed by systemd-cryptsetup-generator with keyfile-erase=on. What happens if the service is run twice, but the key is consumed only the first time? A decrypted keyfile remains in the system. What's the correct approach to avoid such a scenario? Riccardo
