5. Troubleshooting

5.1. RTNETLINK answers: No such file or directory

5.1.1. Phenomenon

tcset command failed with an error message:

• RTNETLINK answers: No such file or directory

• Error: Specified qdisc not found

Example:

$ sudo tcset eth0 --rate 1Mbps
[ERROR] tcconfig: command execution failed
  command=/usr/sbin/tc qdisc add dev eth0 parent 1a1a:2 handle 2873: netem delay 10ms
  stderr=Error: Specified qdisc not found.

5.1.2. Solution

Execute the following command to load sch_netem module. The cause of the error is sch_netem kernel module is not loaded in your system which is required to set up traffic control.

$ sudo modprobe sch_netem

If the command fails with the below message, you need to install an additional kernel module.

Example - Fedora:

$ sudo modprobe sch_netem
modprobe: FATAL: Module sch_netem not found in directory /lib/modules/4.20.11-200.fc29.x86_64

In that case, install kernel-modules-extra package. This package includes the sch_netem module.

Example - Fedora:

$ sudo dnf install -y kernel-modules-extra

Load sch_netem module after the package installation.

$ sudo modprobe sch_netem
$

5.2. RTNETLINK answers: Operation not supported

5.2.1. Phenomenon

tcset command with --direction incoming failed with an error message RTNETLINK answers: Operation not supported.

5.2.2. Solutions

Checking Linux kernel configurations and reconfiguring them if required configurations are disabled.

The cause may be some mandatory kernel configurations are disabled. The following configurations are needed to be enabled to use --direction incoming option.

• CONFIG_IP_ADVANCED_ROUTER

• CONFIG_IP_MULTIPLE_TABLES

• CONFIG_NETFILTER_NETLINK

• CONFIG_NETFILTER_NETLINK_QUEUE

• CONFIG_NETFILTER_NETLINK_LOG

• CONFIG_NF_CT_NETLINK

• CONFIG_NETFILTER_XT_TARGET_MARK

• CONFIG_NET_SCHED

• CONFIG_NET_SCH_INGRESS

• CONFIG_SCSI_NETLINK

e.g. Kernel configurations that enabled the above configurations (Debian)

$ cat /boot/config-3.16.0-4-amd64 | egrep "NETFILTER_NETLINK=|NETFILTER_NETLINK_QUEUE=|NETFILTER_NETLINK_LOG=|NF_CT_NETLINK=|SCSI_NETLINK=|IP_ADVANCED_ROUTER=|NET_SCH_INGRESS=|NET_SCHED=|IP_MULTIPLE_TABLES=|NETFILTER_XT_TARGET_MARK="
CONFIG_IP_ADVANCED_ROUTER=y
CONFIG_IP_MULTIPLE_TABLES=y
CONFIG_NETFILTER_NETLINK=m
CONFIG_NETFILTER_NETLINK_QUEUE=m
CONFIG_NETFILTER_NETLINK_LOG=m
CONFIG_NF_CT_NETLINK=m
CONFIG_NETFILTER_XT_TARGET_MARK=m
CONFIG_NET_SCHED=y
CONFIG_NET_SCH_INGRESS=m
CONFIG_SCSI_NETLINK=y

These configurations need to be either y or m. If some of the configurations are disabled, you need to:

1. enable the kernel configurations

2. build kernel

3. using the compiled kernel image as the boot kernel

Note

The name of the kernel configuration file (/boot/config-3.16.0-4-amd64) differs depending on the environment.