Revert "nixos-container: use systemd-run instead of nsenter"

This reverts commit 7cb100b6833e020d4a4b25c3766cfde507e763e6.

See also #83432.

This appears to break at least the `container`-backend of `nixops`: when
running `switch-to-configuration` within `nixos-container run`, the
running `systemd`-instance gets reloaded which appears to kill the
`systemd-run` command and causes `nixos-container run` to hang.

The full issue is reported in the original PR[1].

[1] https://github.com/NixOS/nixpkgs/pull/67332#issuecomment-604145869

(cherry picked from commit 7f1ba606ac632c50efd33c435aa59e69d4f58acc)

1 files changed, 4 insertions, 4 deletions

diff --git a/pkgs/tools/virtualization/nixos-container/nixos-container.pl b/pkgs/tools/virtualization/nixos-container/nixos-container.pl
index 6e38942cb25..dc05c974bd0 100755
--- a/pkgs/tools/virtualization/nixos-container/nixos-container.pl
+++ b/pkgs/tools/virtualization/nixos-container/nixos-container.pl
@@ -9,6 +9,7 @@ use Getopt::Long qw(:config gnu_getopt);
 use Cwd 'abs_path';
 use Time::HiRes;
 
+my $nsenter = "@utillinux@/bin/nsenter";
 my $su = "@su@";
 
 # Ensure a consistent umask.
@@ -319,10 +320,9 @@ sub restartContainer {
 # Run a command in the container.
 sub runInContainer {
     my @args = @_;
-
-    exec("systemd-run", "--machine", $containerName, "--pty", "--quiet", "--", @args);
-
-    die "cannot run ‘systemd-run’: $!\n";
+    my $leader = getLeader;
+    exec($nsenter, "-t", $leader, "-m", "-u", "-i", "-n", "-p", "--", @args);
+    die "cannot run ‘nsenter’: $!\n";
 }
 
 # Remove a directory while recursively unmounting all mounted filesystems within