Add support for SystemdOptions EFI var to augment /proc/cmdline

In various circumstances, overriding the kernel commandline can be inconvenient.
People have different bootloaders, and e.g. the grub config can be pretty scary.
grubby helps, but it isn't always available.

This option adds an alternative mechanism that can quite convenient on EFI
systems. cmdline settings have higher priority, because they can be (usually)
changed on the bootloader prompt.

$SYSTEMD_EFI_OPTIONS can be used to override, same as $SYSTEMD_PROC_CMDLINE.

1 files changed, 7 insertions, 4 deletions

diff --git a/docs/ENVIRONMENT.md b/docs/ENVIRONMENT.md
index 838cc7e4cf..f9025247d8 100644
--- a/docs/ENVIRONMENT.md
+++ b/docs/ENVIRONMENT.md
@@ -36,10 +36,13 @@ All tools:
 * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
   will print latency information at runtime.
 
-* `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel
-  command line instead of the actual one readable from /proc/cmdline. This is
-  useful for debugging, in order to test generators and other code against
-  specific kernel command lines.
+* `$SYSTEMD_PROC_CMDLINE` — if set, the contents are used as the kernel command
+  line instead of the actual one in /proc/cmdline. This is useful for
+  debugging, in order to test generators and other code against specific kernel
+  command lines.
+
+* `$SYSTEMD_EFI_OPTIONS` — if set, used instead of the string in SystemdOptions
+  EFI variable. Analogous to `$SYSTEMD_PROC_CMDLINE`.
 
 * `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
   This is useful for debugging and testing initrd-only programs in the main