Differences

This shows you the differences between two versions of the page.

--- doc:appunti:linux:sa:if_rename [2021/05/13 17:14] – [With Debian 10 Buster] 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:
-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
+#/etc/systemd/network/10-persistent-lan0.link
+[Match]
+MACAddress=00:e0:4c:88:53:02
+[Link]
+Name=lan0
 </file>
-Another methos should be to create a file **/etc/systemd/network/10-persistent-net.link** with something like
+**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.
+**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>
-#/etc/systemd/network/10-persistent-net.link
 [Match]
 MACAddress=00:e0:4c:88:53:02
+OriginalName=eth*
 [Link]
 Name=lan0
 </file>
-Both seems to work, unfortunately on my XFCE environment, the **NetworkManager** stepped into the play, reverting back the name:
+==== 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 ====
+Both methods seen above seem to work, unfortunately on my XFCE environment, the **NetworkManager** stepped into the play, reverting back the name:
 <file>
@@ Line 29: / Line 66: @@
 </file>
-To keep it simple, I choosed the kernel override option in **/etc/default/grub**:
+If you want to **manage the interface using NetworkManager** from the user session, be sure that the interface is not referred by **/etc/network/interfaces** or any snippet file into ''/etc/network/interfaces.d/''. If the interface is configured by ''/etc/network/interfaces'', NetworkManger will ignore it, labelling as //unmanaged//.
+==== Use the old naming schema (eth0, ...) ====
+If you want to use the old naming schema (eth0, eth1, ...) enable the kernel override option in **/etc/default/grub**:
 <file>
@@ Line 37: / Line 78: @@
 Followed by **update-grub** and **reboot**.
-If you want to **manage the interface using NetworkManager** from the user session, be sure that the interface is not referred by **/etc/network/interfaces** or any snippet file into ''/etc/network/interfaces.d/''. If the interface is configured by ''/etc/network/interfaces'', NetworkManger will ignore it, labelling as //unmanaged//.
+Beware that by using that schema the card's assigned name depends upon the time when the kernel discover the interfaces, in some cases you may find the names swapped after a reboot, even if the Ethernet cards are fixed built-in.
 ===== How it worked in the old days of Debian 4 Etch =====
@@ Line 108: / Line 149: @@
 SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="00:18:e7:22:0b:f7", NAME="eth1"
 </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**: Il file con le regole udev viene ignorato comunque in **Debian 11**.
 ===== Debian 9 Network Interface Naming =====