Check for systemd environment variables that are too long

Issue #3403. For the case of $PATH being too long, we could call
buildEnv automatically.

1 files changed, 3 insertions, 1 deletions

diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index 14caa5d360d5..777c1ea74d88 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -317,7 +317,9 @@ let
         ''
           [Service]
           ${let env = cfg.globalEnvironment // def.environment;
-            in concatMapStrings (n: "Environment=\"${n}=${getAttr n env}\"\n") (attrNames env)}
+            in concatMapStrings (n:
+              let s = "Environment=\"${n}=${getAttr n env}\"\n";
+              in if stringLength s >= 2048 then throw "The value of the environment variable ‘${n}’ in systemd service ‘${name}.service’ is too long." else s) (attrNames env)}
           ${if def.reloadIfChanged then ''
             X-ReloadIfChanged=true
           '' else if !def.restartIfChanged then ''