[pve-devel] [PATCH container] fix #4460: setup: centos: create /etc/hostname if it does not exist

[Friedrich Weber <f.weber@proxmox.com>]

Previously, Setup/CentOS.pm only wrote to /etc/hostname if the file
already existed. Many CT templates of Redhat-derived distros do not
contain that file, so the containers ended up without /etc/hostname.
This caused systemd-hostnamed to report the "static hostname" to be
empty. If networking is handled by NetworkManager, the empty static
hostname caused DHCP requests to be sent without the "Hostname" field,
as reported in #4460.

With this fix, Setup/CentOS.pm creates /etc/hostname if it does not
exist, so NetworkManager correctly reads the hostname and includes it in
DHCP requests.

Manually tested with the following CT templates (checking that
/etc/hostname exists and DHCP requests include the hostname):

* Distros using NetworkManager:
 - Alma Linux 9 (almalinux-9-default_20221108_amd64.tar.xz)
 - CentOS 8 (centos-8-default_20201210_amd64.tar.xz)
 - CentOS 9 Stream (centos-9-stream-default_20221109_amd64.tar.xz)
 - Rocky Linux 9 (rockylinux-9-default_20221109_amd64.tar.xz)
* Distros using network-scripts (here, DHCP requests already contained the
hostname without this fix, as network-scripts does not rely on
systemd-hostnamed):
 - Alma Linux 8 (almalinux-8-default_20210928_amd64.tar.xz)
 - CentOS 7 (centos-7-default_20190926_amd64.tar.xz)
 - CentOS 8 Stream (centos-8-stream-default_20220327_amd64.tar.xz)
 - Rocky Linux 8 (rockylinux-8-default_20210929_amd64.tar.xz)

Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
---

Question: This will cause Setup/CentOS.pm to create /etc/hostname also
in already-existing containers. I don't think this should any cause
issues for users, but I'm not sure. What do you think?

 src/PVE/LXC/Setup/CentOS.pm                | 5 ++---
 src/test/test-centos6-001/etc/hostname.exp | 1 +
 src/test/test-centos6-002/etc/hostname.exp | 1 +
 src/test/test-centos8-001/etc/hostname.exp | 1 +
 4 files changed, 5 insertions(+), 3 deletions(-)
 create mode 100644 src/test/test-centos6-001/etc/hostname.exp
 create mode 100644 src/test/test-centos6-002/etc/hostname.exp
 create mode 100644 src/test/test-centos8-001/etc/hostname.exp

diff --git a/src/PVE/LXC/Setup/CentOS.pm b/src/PVE/LXC/Setup/CentOS.pm
index 00fecc6..1d31cee 100644
--- a/src/PVE/LXC/Setup/CentOS.pm
+++ b/src/PVE/LXC/Setup/CentOS.pm
@@ -157,9 +157,8 @@ sub set_hostname {
 
     $self->update_etc_hosts($hostip, $oldname, $hostname, $searchdomains);
 
-    if ($self->ct_file_exists($hostname_fn)) {
-	$self->ct_file_set_contents($hostname_fn, "$hostname\n");
-    }
+    # Always write /etc/hostname, even if it does not exist yet
+    $self->ct_file_set_contents($hostname_fn, "$hostname\n");
 
     if ($self->ct_file_exists($sysconfig_network)) {
 	my $data = $self->ct_file_get_contents($sysconfig_network);
diff --git a/src/test/test-centos6-001/etc/hostname.exp b/src/test/test-centos6-001/etc/hostname.exp
new file mode 100644
index 0000000..a5bce3f
--- /dev/null
+++ b/src/test/test-centos6-001/etc/hostname.exp
@@ -0,0 +1 @@
+test1
diff --git a/src/test/test-centos6-002/etc/hostname.exp b/src/test/test-centos6-002/etc/hostname.exp
new file mode 100644
index 0000000..180cf83
--- /dev/null
+++ b/src/test/test-centos6-002/etc/hostname.exp
@@ -0,0 +1 @@
+test2
diff --git a/src/test/test-centos8-001/etc/hostname.exp b/src/test/test-centos8-001/etc/hostname.exp
new file mode 100644
index 0000000..a5bce3f
--- /dev/null
+++ b/src/test/test-centos8-001/etc/hostname.exp
@@ -0,0 +1 @@
+test1
-- 
2.30.2