runtime: Warn if XDG_RUNTIME_DIR is set but is not writable.

[NO TESTS NEEDED]

Signed-off-by: Aditya Rajan <[email protected]>

libpod/runtime.go

@@ -15,6 +15,8 @@ import (
 	"syscall"
 	"time"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/containers/buildah/pkg/parse"
 	"github.com/containers/common/libimage"
 	"github.com/containers/common/pkg/config"
@@ -328,6 +330,16 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (retErr error) {
 
 	runtime.mergeDBConfig(dbConfig)
 
+	unified, _ := cgroups.IsCgroup2UnifiedMode()
+	if unified && rootless.IsRootless() && !systemd.IsSystemdSessionValid(rootless.GetRootlessUID()) {
+		// If user is rootless and XDG_RUNTIME_DIR is found, podman will not proceed with /tmp directory
+		// it will try to use existing XDG_RUNTIME_DIR
+		// if current user has no write access to XDG_RUNTIME_DIR we will fail later
+		if unix.Access(runtime.storageConfig.RunRoot, unix.W_OK) != nil {
+			logrus.Warnf("XDG_RUNTIME_DIR is pointing to a path which is not writable. Most likely podman will fail.")
+		}
+	}
+
 	logrus.Debugf("Using graph driver %s", runtime.storageConfig.GraphDriverName)
 	logrus.Debugf("Using graph root %s", runtime.storageConfig.GraphRoot)
 	logrus.Debugf("Using run root %s", runtime.storageConfig.RunRoot)

troubleshooting.md

@@ -881,3 +881,29 @@ def signal_listener():
 if __name__ == "__main__":
     signal_listener()
 ```
+### 30) Podman run fails with `ERRO[0000] XDG_RUNTIME_DIR directory "/run/user/0" is not owned by the current user` or `Error: error creating tmpdir: mkdir /run/user/1000: permission denied`.
+
+A failure is encountered when performing `podman run` with a warning `XDG_RUNTIME_DIR is pointing to a path which is not writable. Most likely podman will fail.`
+
+#### Symptom
+
+A rootless container is being invoked with cgroup configuration as `cgroupv2` for user with missing or invalid **systemd session**.
+
+Example cases
+```bash
+# su user1 -c 'podman images'
+ERRO[0000] XDG_RUNTIME_DIR directory "/run/user/0" is not owned by the current user
+```
+```bash
+# su - user1 -c 'podman images'
+Error: error creating tmpdir: mkdir /run/user/1000: permission denied
+```
+
+#### Solution
+
+Podman expects a valid login session for the `rootless+cgroupv2` use-case. Podman execution is expected to fail if the login session is not present. In most cases, podman will figure out a solution on its own but if `XDG_RUNTIME_DIR` is pointing to a path that is not writable execution will most fail. Typical scenarious of such cases are seen when users are trying to use Podman with `su - <user> -c '<podman-command>`, or `sudo -l` and badly configured systemd session.
+
+Resolution steps
+
+* Before invoking Podman command create a valid login session for your rootless user using `loginctl enable-linger <username>`
+* If `loginctl` is unavailable you can also try logging in via `ssh` i.e `ssh <username>@localhost`.