add chhostname.py example

1 files changed, 60 insertions, 0 deletions

diff --git a/examples/chhostname.py b/examples/chhostname.py
new file mode 100755
index 0000000..bf174e6
--- /dev/null
+++ b/examples/chhostname.py
@@ -0,0 +1,60 @@
+#!/usr/bin/python3
+# Copyright 2024 Helmut Grohne <helmut@subdivi.de>
+# SPDX-License-Identifier: GPL-3
+
+"""Unshare a UTS (and user and mount) namespace and change the hostname."""
+
+import os
+import pathlib
+import socket
+import sys
+import tempfile
+
+if __file__.split("/")[-2:-1] == ["examples"]:
+    sys.path.insert(0, "/".join(__file__.split("/")[:-2]))
+
+import linuxnamespaces
+
+
+def change_file(location: pathlib.Path, content: bytes | str) -> None:
+    if isinstance(content, str):
+        content = content.encode("ascii")
+    try:
+        st = location.stat()
+    except FileNotFoundError as err:
+        raise ValueError(
+            f"cannot change non-existent file: {location!r}"
+        ) from err
+    if st.st_size == len(content) and location.read_bytes() == content:
+        return
+    with tempfile.NamedTemporaryFile() as tfile:
+        tfile.write(content)
+        # In Python >= 3.12, we should set delete_on_close=False rather than
+        # closing the underlying file object behind tempfile's back.
+        tfile.file.close()
+        linuxnamespaces.bind_mount(tfile.name, location)
+
+
+def main() -> None:
+    hostname = sys.argv[1]
+    linuxnamespaces.unshare_user_idmap(
+        [linuxnamespaces.IDMapping.identity(os.getuid())],
+        [linuxnamespaces.IDMapping.identity(os.getgid())],
+        linuxnamespaces.CloneFlags.NEWUSER
+        | linuxnamespaces.CloneFlags.NEWNS
+        | linuxnamespaces.CloneFlags.NEWUTS,
+    )
+    socket.sethostname(hostname)
+    etc = pathlib.Path("/etc")
+    change_file(etc / "hostname", f"{hostname}\n")
+    change_file(
+        etc / "hosts",
+        f"""127.0.0.1 {hostname} localhost
+::1 {hostname} localhost
+""",
+    )
+    os.execlp(os.environ["SHELL"], os.environ["SHELL"])
+
+
+if __name__ == "__main__":
+    main()