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--- doc:appunti:linux:sa:if_rename [2023/12/15 10:23] – niccolo
+++ doc:appunti:linux:sa:if_rename [2024/06/21 17:54] (current) – [Beware of initramfs image] niccolo
@@ Line 3: / Line 3: @@
 ===== With Debian 10 Buster =====
-According some sources, there is at least two methods to rename a network interface e.g. from **enx00e04c885302** to something more human like **lan0** or the plain old **eth0**.
+How to rename a network interface from e.g. **enx00e04c885302** to something more human like **lan0**? The preferred method is to create a file **/etc/systemd/network/10-persistent-lan0.link** (one file for each interface to be renamed) with something like this:
-**WARNING**: This method does not work in Debian 12. The simplest method should be to add a line into **/etc/network/interfaces** (or to create a new file **/etc/network/interfaces.d/local**) with the following:
-<file>
-rename enx00e04c885302=lan0
-</file>
-Another methos should be to create a file **/etc/systemd/network/10-persistent-lan0.link** (one file for each interface to be renamed) with something like this:
 <file>
@@ Line 21: / Line 13: @@
 </file>
-The systemd method has a problem if you need to create a **VLAN**. When the system creates e.g. the **lan.602**, its MAC address matches the systemd snippet, so systemd tries to assign to it the name **lan** but the name already exists, so the interface remains with a temporary name e.g. **rename5**.
+**WARNING**: You cannot use this method to safely assign the default kernel names (''eth0'', ''eth1'', ...) in your preferred order; this is because if systemd tries to rename an interface using a name which is already assigned by the kernel (e.g. it tries to swap ''eth0'' and ''eth1''), it fails. So the target **Name** must not potentially conflict with the names assigned by the kernel.
-A workaround can be the following: tell the kernel to use the old eth0 schema (passing the **net.ifnames=0** option), then instruct systemd to act only on **%%eth*%%** network interfaces:
+**WARNING**: This method has an additional problem if you need to create a **VLAN**. When the system creates e.g. the **lan.602**, its MAC address matches the systemd snippet, so systemd tries to assign to it the name (**lan0** in the example above) but the name already exists, so the interface remains with a temporary name e.g. **rename5**.
+A workaround can be the following: tell the kernel to use the old ''ethX'' schema (passing the **net.ifnames=0** option), then instruct systemd to act only on **%%eth*%%** network interfaces:
 <file>
@@ Line 32: / Line 26: @@
 Name=lan0
 </file>
+==== Beware of initramfs image ====
+:!: If you have some files in **/etc/systemd/network/** to rename network interfaces and you update the **initramfs image** (e.g. by running the **update-initramfs** tool), a copy of these files are placed into the image itself (under the path **usr/lib/systemd/network/**).
+These files are considered by ''init'' before it considers the content of **/etc/systemd/network/**. When the latter files are processed, some renaming may have already occurred and rules may not longer apply or may fail.
+So it is always advisable to **update the initramfs** whenever you update the content of **/etc/systemd/network/**.
+<code>
+update-initramfs -k all -u
+</code>
+=== How to unpack the iniramfs image to inspect its content ===
+In **Debian 12** the iniramfs image may be composed by two appended cpio archives. The first containing the Intel microcode in //ASCII cpio archive// format, and the second containing the actual initramfs as a //Zstandard compressed cpio archive//. To extract both, do the following:
+Extract **the microcode part** (take note of the number of blocks printed on stderr):
+<code>
+cat /boot/initrd.img-6.1.0-21-amd64 | cpio --extract --make-directories  --no-absolute-filenames
+blocks
+</code>
+Make a copy of **the initramfs part** stripping the microcode and decompress it:
+<code>
+dd if=/boot/initrd.img-6.1.0-21-amd64 of=initramfs.img.zst bs=512 skip=14080
+unzstd initramfs.img.zst --stdout | cpio --extract --make-directories  --no-absolute-filenames
+</code>
 ==== NetworkManager interfering with rename ====
@@ Line 126: / Line 150: @@
 </file>
-**ATTENZIONE**: Pare che **il file con le regole udev viene ignorato** se manca l'opzione **net.ifnames=0** nella cmdline del kernel! Questo almeno è accaduto con Debian 11.7 e kernel 5.10.0-23-amd64.
+:!: **ATTENZIONE**: Pare che **il file con le regole udev viene ignorato** se manca l'opzione **net.ifnames=0** nella cmdline del kernel! Questo almeno è accaduto con Debian 11.7 e kernel 5.10.0-23-amd64.
+:!: **ATTENZIONE**: Il file con le regole udev viene ignorato comunque in **Debian 11**.
 ===== Debian 9 Network Interface Naming =====