linux bonding - changing params if statically linked

There are two APIs to handle bonding interfaces, in addition to the obsolete commands (on Linux) ifconfig and ifenslave, which probably aren't able to create a new bond interfaces (and thus require the bonding module's max_bonds parameter to be non zero).

• kernel's (rt)netlink API: through most of the modern commands provided by iproute2 including the ip link command.

• kernel's sysfs API via pseudo-files: usually mounted in /sys/.

I can note that "recent" versions of ifenslave actually rely on the the sysfs API and a little on the rtnetlink API through ip link.

You should probably configure bonding to create zero interface instead of the default one or two: this is an historical feature that became obsolete with these two APIs. These interface can be created or removed dynamically later. Of course for a very minimal system leaving it or setting it to create the required needed number is still an option. Adding this to the kernel command line options (usually found in /etc/default/grub's GRUB_CMDLINE_LINUX= entry, but doing this correctly might depend on the distribution) should do it:

bonding.max_bonds=0 

• Configuring Bonding Manually with iproute2 (ip link):

  Warning: the linked documentation is quite incomplete/obsolete and doesn't show that most if not all of the bonding features are available through ip link.

  You can create delete alter settings enslave etc. with the right ip link command. This command should include the keywords type bond whenever it has to specify a specific bond option after them.

  command syntax reminder, to display specific bond settings:

  ip link add type bond help 

  example (interfaces must be down before being enslaved, but can be set such in the same single command in case former state is not known):

  ip link add dev mybond0 type bond mode active-backup miimon 100 ip link set dev eth0 down master mybond0 ip link set dev eth1 down master mybond0 ip link set dev mybond0 up ip link set dev eth0 up ip link set dev eth1 up 

  changing settings:

  ip link set dev mybond0 type bond miimon 200 

  ifenslave equivalent:

  ip link set dev mybond0 type bond active_slave eth1 

  some settings can't be changed while there are any enslaved devices. Eg, redefining the bond type:

  # ip link set dev mybond0 type bond mode balance-rr RTNETLINK answers: Directory not empty 

  enslaved devices can be set free with:

  ip link set dev eth0 nomaster 

  and the bond device can be deleted with:

  ip link delete dev mybond0 

  various information related to a bond device (or to a bond_slave device) can be seen with the additional -details option. At some point using JSON output can be easier for scripts (eg, this Q/A: iproute2: How to display the TYPE of a network devices?).

  ip -detail link show dev mybond0 ip -detail link show dev eth0 ip -detail link show dev eth1 

• Configuring Bonding Manually via Sysfs

  I don't think using this API makes much sense today unless a specific feature wasn't made available through ip link. It was probably created before iproute2 tools could handle all of it. Maybe reading from it could still help in case the tools on a restricted/embedded system don't have anymore access to an ip link command, but even this seems unlikely.

  As described in the linked documentation, you can create and delete bonding interfaces through /sys/class/net/bonding_masters which is present whenever the bonding module is present (here as built-in).

  Here are the equivalent commands from above, simply using echo ... > ... from a root shell (or having to work around redirections with sudo echo ... | tee ...):

  echo +mybond0 > /sys/class/net/bonding_masters echo active-backup > /sys/class/net/mybond0/bonding/mode echo 100 > /sys/class/net/mybond0/bonding/miimon 

  I don't see any way to set interfaces up or down through sysfs anyway. To stay safe:

  ip link set dev eth0 down ip link set dev eth1 down echo +eth0 > /sys/class/net/mybond0/bonding/slaves echo +eth1 > /sys/class/net/mybond0/bonding/slaves 

  Again, there's no other way:

  ip link set dev mybond0 up ip link set dev eth0 up ip link set dev eth1 up 

  Then continuing like the previous example:

  echo 200 > /sys/class/net/mybond0/bonding/miimon echo eth1 > /sys/class/net/mybond0/bonding/active_slave # echo balance-rr > /sys/class/net/mybond0/bonding/mode bash: echo: write error: Directory not empty echo -eth0 > /sys/class/net/mybond0/bonding/slaves echo -mybond0 > /sys/class/net/bonding_masters 

  Specific bonding information is available there:

  cat /sys/class/net/bonding_masters grep ^ /sys/class/net/mybond0/bonding/* grep ^ /sys/class/net/eth0/bonding_slave/* grep ^ /sys/class/net/eth1/bonding_slave/*