[PATCH 1/2] add script to check if the current environment supports rootless builds

[Felix Moessbauer]

Running builds in rootless mode has a lot of non obvious pre conditions.
To help the user check if his system is configured correctly, we provide
a script that checks the needed features. If a feature is missing, it
issues an error regarding what likely is the root cause.

Signed-off-by: Felix Moessbauer <felix.mo...@siemens.com>
---
scripts/isar-check-rootless | 46 +++++++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)
create mode 100755 scripts/isar-check-rootless

diff --git a/scripts/isar-check-rootless b/scripts/isar-check-rootless
new file mode 100755
index 00000000..61a2a2e3
--- /dev/null
+++ b/scripts/isar-check-rootless
@@ -0,0 +1,46 @@
+#!/bin/sh
+# Copyright (C) 2026 Siemens AG
+# SPDX-License-Identifier: MIT
+#
+# Helper script to check if the current environment supports unprivileged
+# rootless builds with unshare.
+# Returns 0 if supported, otherwise returns 1 and prints an error message to stderr.
+
+if ! run_privileged_cmd=$(bitbake-getvar -q --value RUN_PRIVILEGED_CMD); then
+ echo "error: cannot determine RUN_PRIVILEGED_CMD from BitBake" >&2
+ exit 1
+fi
+
+if ! ${run_privileged_cmd} /bin/sh <<'EOF'
+ failed=0
+
+ fail() {
+ echo "error: $1" >&2
+ echo " likely cause: $2" >&2
+ failed=1
+ }
+
+ mountpoint=$(mktemp -d)
+ if [ -n "$mountpoint" ]; then
+ if ! mount -t proc proc "$mountpoint"; then
+ fail "cannot mount procfs in the user namespace" \
+ "procfs is over-mounted by the container runtime, or the host security policy blocks procfs mounts"
+ else
+ umount "$mountpoint"
+ fi
+ rmdir "$mountpoint"
+ fi
+
+ if ! setpriv --reuid=nobody --regid=nogroup --clear-groups /usr/bin/true; then
+ fail "cannot execute as nobody:nogroup in the user namespace" \
+ "the subuid / subgid ID range is too small or incomplete"
+ fi
+
+ exit "$failed"
+EOF
+then
+ echo "error: unprivileged rootless builds are not supported; see the checks above" >&2
+ exit 1
+fi
+
+echo "unprivileged rootless builds are supported"
--
2.55.0

[Felix Moessbauer]

Currently only the requirements for privileged execution are documented.
As we now support rootless execution as well, document this - along with
the requirements check script.

Signed-off-by: Felix Moessbauer <felix.mo...@siemens.com>
---

doc/user_manual.md | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/doc/user_manual.md b/doc/user_manual.md
index cb47c157..8d12a992 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -140,9 +140,15 @@ To run images built for QEMU, you also need to install the related package:
apt install qemu
```

-### Setup Sudo
+Isar has two execution modes: privileged (default), and rootless. The mode
+only determines how Isar obtains the privileges needed during a build; it does
+not affect the generated artifacts. The following sections describe their
+respective host requirements and setup.

-Isar requires `sudo` rights without password to work with `chroot`. To add them, use the following steps:
+### Privileged Builds
+
+Privileged execution requires `sudo` rights without password to work with `chroot`.
+To add them, use the following steps:
```
# visudo
```
@@ -154,6 +160,27 @@ In the editor, allow the current user to run sudo without a password, e.g.:
Replace `<user>` with your username. Use the tab character between the username and parameters.
The second line will make sure your proxy settings will not get lost when using `sudo`. Include it if you are in the unfortunate position to having to deal with that.

+### Rootless Builds
+
+As an alternative to the privileged `schroot` backend, Isar can build using unprivileged user namespaces.
+To verify that the current host and user support rootless builds, run the
+following command after [initializing the build directory](#initialize-the-build-directory):
+
+```
+$ scripts/isar-check-rootless
+```
+
+Enable rootless builds in `conf/local.conf`:
+
+```
+ISAR_ROOTLESS = "1"
+```
+
+Files produced inside a rootless namespace can have ownership that the calling
+user cannot remove directly. Use `scripts/isar-clean-builddir --rootless <dir>`
+to clean a build directory with mixed ownership. When using a container, run
+the cleanup script from the same container environment that created the files.
+
### Check out Isar

Clone the Isar repository:
--
2.55.0

[Felix Moessbauer]

Running builds in rootless mode has a lot of non obvious pre conditions.
To help the user check if his system is configured correctly, we provide
a script that checks the needed features. If a feature is missing, it
issues an error regarding what likely is the root cause.

Signed-off-by: Felix Moessbauer <felix.mo...@siemens.com>
---

Changes since v1:
- ensure rootless is enabled before calling bitbake-getvar
- add -v option to print the RUN_PRIVILEGED_CMD variable
scripts/isar-check-rootless | 55 +++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)

create mode 100755 scripts/isar-check-rootless

diff --git a/scripts/isar-check-rootless b/scripts/isar-check-rootless
new file mode 100755

index 00000000..b5197111
--- /dev/null
+++ b/scripts/isar-check-rootless
@@ -0,0 +1,55 @@

+#!/bin/sh
+# Copyright (C) 2026 Siemens AG
+# SPDX-License-Identifier: MIT
+#
+# Helper script to check if the current environment supports unprivileged
+# rootless builds with unshare.
+# Returns 0 if supported, otherwise returns 1 and prints an error message to stderr.
+

+verbose=0
+if [ "$1" = "-v" ]; then
+ verbose=1
+fi
+
+if ! run_privileged_cmd=$( \
+ BB_ENV_PASSTHROUGH_ADDITIONS="${BB_ENV_PASSTHROUGH_ADDITIONS} ISAR_ROOTLESS" \
+ ISAR_ROOTLESS=1 bitbake-getvar -q --value RUN_PRIVILEGED_CMD); then

+ echo "error: cannot determine RUN_PRIVILEGED_CMD from BitBake" >&2
+ exit 1
+fi
+

+[ "$verbose" = 0 ] || echo "RUN_PRIVILEGED_CMD: $run_privileged_cmd" >&2

[Felix Moessbauer]

Currently only the requirements for privileged execution are documented.
As we now support rootless execution as well, document this - along with
the requirements check script.

Signed-off-by: Felix Moessbauer <felix.mo...@siemens.com>
---

doc/user_manual.md | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/doc/user_manual.md b/doc/user_manual.md

index dcc3f560..6c6814dd 100644

[Zhihang Wei]

Applied to next, thanks.

Zhihang