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eBPF monitoring with Netdata

Netdata's extended Berkeley Packet Filter (eBPF) collector monitors kernel-level metrics for file descriptors, virtual filesystem IO, and process management on Linux systems. You can use our eBPF collector to analyze how and when a process accesses files, when it makes system calls, whether it leaks memory or creating zombie processes, and more.

Netdata's eBPF monitoring toolkit uses two custom eBPF programs. The default, called entry, monitors calls to a variety of kernel functions, such as do_sys_open, __close_fd, vfs_read, vfs_write, _do_fork, and more. The return program also monitors the return of each kernel functions to deliver more granular metrics about how your system and its applications interact with the Linux kernel.

eBPF monitoring can help you troubleshoot and debug how applications interact with the Linux kernel. See our guide on troubleshooting apps with eBPF metrics for configuration and troubleshooting tips.

An example of VFS charts, made possible by the eBPF collector plugin
An example of VFS charts made possible by the eBPF collector plugin.

Enable the collector on Linux

The eBPF collector is installed and enabled by default on most new installations of the Agent. The eBPF collector does not currently work with static build installations, but improved support is in active development.

eBPF monitoring only works on Linux systems and with specific Linux kernels, including all kernels newer than 4.11.0, and all kernels on CentOS 7.6 or later.

If your Agent is v1.22 or older, you may to enable the collector yourself. See the configuration section for details.

Charts

The eBPF collector creates an eBPF menu in the Agent's dashboard along with three sub-menus: File, VFS, and Process. All the charts in this section update every second. The collector stores the actual value inside of its process, but charts only show the difference between the values collected in the previous and current seconds.

File

This group has two charts demonstrating how software interacts with the Linux kernel to open and close file descriptors.

File descriptor

This chart contains two dimensions that show the number of calls to the functions do_sys_open and __close_fd. Most software do not commonly call these functions directly, but they are behind the system calls open(2), openat(2), and close(2).

File error

This chart shows the number of times some software tried and failed to open or close a file descriptor.

VFS

A virtual file system (VFS) is a layer on top of regular filesystems. The functions present inside this API are used for all filesystems, so it's possible the charts in this group won't show all the actions that occurred on your system.

Deleted objects

This chart monitors calls for vfs_unlink. This function is responsible for removing objects from the file system.

IO

This chart shows the number of calls to the functions vfs_read and vfs_write.

IO bytes

This chart also monitors vfs_read and vfs_write, but instead shows the total of bytes read and written with these functions.

The Agent displays the number of bytes written as negative because they are moving down to disk.

IO errors

The Agent counts and shows the number of instances where a running program experiences a read or write error.

Process

For this group, the eBPF collector monitors process/thread creation and process end, and then displays any errors in the following charts.

Process thread

Internally, the Linux kernel treats both processes and threads as tasks. To create a thread, the kernel offers a few system calls: fork(2), vfork(2) and clone(2). In turn, each of these system calls use the function _do_fork. To generate this chart, the eBPF collector monitors _do_fork to populate the process dimension, and monitors sys_clone to identify threads.

Exit

Ending a task requires two steps. The first is a call to the internal function do_exit, which notifies the operating system that the task is finishing its work. The second step is to release the kernel information with the internal function release_task. The difference between the two dimensions can help you discover zombie processes.

Task error

The functions responsible for ending tasks do not return values, so this chart contains information about failures on process and thread creation.

Configuration

Enable or disable the entire eBPF collector by editing netdata.conf.

cd /etc/netdata/   # Replace with your Netdata configuration directory, if not /etc/netdata/
./edit-config netdata.conf

To enable the collector, scroll down to the [plugins] section ensure the relevant line references ebpf (not ebpf_process), is uncommented, and is set to yes.

[plugins]
   ebpf = yes

You can also configure the eBPF collector's behavior by editing ebpf.conf.

cd /etc/netdata/   # Replace with your Netdata configuration directory, if not /etc/netdata/
./edit-config ebpf.conf

[global]

The [global] section defines settings for the whole eBPF collector.

ebpf load mode

The collector has two different eBPF programs. These programs monitor the same functions inside the kernel, but they monitor, process, and display different kinds of information.

By default, this plugin uses the entry mode. Changing this mode can create significant overhead on your operating system, but also offer valuable information if you are developing or debugging software. The ebpf load mode option accepts the following values: ​

  • entry: This is the default mode. In this mode, the eBPF collector only monitors calls for the functions described in the sections above, and does not show charts related to errors.
  • return: In the return mode, the eBPF collector monitors the same kernel functions as entry, but also creates new charts for the return of these functions, such as errors. Monitoring function returns can help in debugging software, such as failing to close file descriptors or creating zombie processes.

Integration with apps.plugin

The eBPF collector also creates charts for each running application through an integration with the apps.plugin. This integration helps you understand how specific applications interact with the Linux kernel.

When the integration is enabled, your dashboard will also show the following charts using low-level Linux metrics:

  • eBPF syscall
    • Number of calls to open files.
    • Number of files closed.
    • Number of calls to delete files.
    • Number of calls to vfs_write.
    • Number of calls to vfs_read.
    • Number of bytes written trough vfs_write
    • Number of bytes read trough vfs_read
    • Number of process created trough do_fork
    • Number of threads created trough do_fork or __x86_64_sys_clone, depending on your system's kernel version.
    • Number of times that a process called do_exit.
    • Number of calls to open files that returned errors.
    • Number of calls to close files that returned errors.
    • Number of calls to read a file that returned errors.
    • Number of calls to read a file that returned errors.
  • eBPF net
    • Number of bytes transmited per seconds.

If you want to disable the integration with apps.plugin along with the above charts, change the setting disable apps to yes.

[global]
   disable apps = yes

[ebpf programs]

The eBPF collector enables and runs the following eBPF programs by default:

  • process: This eBPF program creates charts that show information about process creation, VFS IO, and files removed. When in return mode, it also creates charts showing errors when these operations are executed.
  • network viewer: This eBPF program creates charts with information about TCP and UDP functions, including the bandwidth consumed by each.

[network viewer]

You can configure the information shown on outbound and inbound charts with the settings in this section.

[network viewer]
    maximum dimensions = 500
    resolve hostname ips = no
    ports = 1-1024 !145 !domain
    hostnames = !example.com
    ips = !127.0.0.1/8 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 fc00::/7

When you define a ports setting, Netdata will collect network metrics for that specific port. For example, if you write ports = 19999, Netdata will collect only connections for itself. The hostnames setting accepts
simple patterns. The ports, and ips settings accept negation (!) to deny specific values or asterisk alone to define all values.

In the above example, Netdata will collect metrics for all ports between 1 and 443, with the exception of 53 (domain) and 145.

The following options are available:

  • ports: Define the destination ports for Netdata to monitor.
  • hostnames: The list of hostnames that can be resolved to an IP address.
  • ips: The IP or range of IPs that you want to monitor. You can use IPv4 or IPv6 addresses, use dashes to define a range of IPs, or use CIDR values. The default behavior is to only collect data for private IP addresess, but this can be changed with the ips setting.

By default, Netdata displays up to 500 dimensions on network viewer charts. If there are more possible dimensions, they will be bundled into the other dimension. You can increase the number of shown dimensions by changing the maximum dimensions setting.

The dimensions for the traffic charts are created using the destination IPs of the sockets by default. This can be changed setting resolve hostname ips = yes and restarting Netdata, after this Netdata will create dimensions using the hostnames every time that is possible to resolve IPs to their hostnames.

[service name]

Netdata uses the list of services in /etc/services to plot network viewer charts. If this file does not contain the name for a particular service you use in your infrastructure, you will need to add it to the [service name] section.

For example, Netdata's default port (19999) is not listed in /etc/services. To associate that port with the Netdata service in network viewer charts, and thus see the name of the service instead of its port, define it:

[service name]
    19999 = Netdata

Troubleshooting

If the eBPF collector does not work, you can troubleshoot it by running the ebpf.plugin command and investigating its output.

cd /usr/libexec/netdata/plugins.d/
sudo -u netdata bash
./ebpf.plugin

You can also use grep to search the Agent's error.log for messages related to eBPF monitoring.

grep -i ebpf /var/log/netdata/error.log

Confirm kernel compatibility

The eBPF collector only works on Linux systems and with specific Linux kernels. We support all kernels more recent than 4.11.0, and all kernels on CentOS 7.6 or later.

You can run our helper script to determine whether your system can support eBPF monitoring.

curl -sSL https://raw.githubusercontent.com/netdata/kernel-collector/master/tools/check-kernel-config.sh | sudo bash

If this script returns no output, your system is ready to compile and run the eBPF collector.

If you see a warning about a missing kerkel configuration (KPROBES KPROBES_ON_FTRACE HAVE_KPROBES BPF BPF_SYSCALL BPF_JIT), you will need to recompile your kernel to support this configuration. The process of recompiling Linux kernels varies based on your distribution and version. Read the documentation for your system's distribution to learn more about the specific workflow for recompiling the kernel, ensuring that you set all the necessary

Mount debugfs and tracefs

The eBPF collector also requires both the tracefs and debugfs filesystems. Try mounting the tracefs and debugfs filesystems using the commands below:

sudo mount -t debugfs nodev /sys/kernel/debug
sudo mount -t tracefs nodev /sys/kernel/tracing

If they are already mounted, you will see an error. You can also configure your system's /etc/fstab configuration to mount these filesystems on startup. More information can be found in the ftrace documentation.

Performance

Because eBPF monitoring is complex, we are evaluating the performance of this new collector in various real-world conditions, across various system loads, and when monitoring complex applications.

Our initial testing shows the performance of the eBPF collector is nearly identical to our apps.plugin collector, despite collecting and displaying much more sophisticated metrics. You can now use the eBPF to gather deeper insights without affecting the performance of your complex applications at any load.

SELinux

When SELinux is enabled, it may prevent ebpf.plugin from starting correctly. Check the Agent's error.log file for errors like the ones below:

2020-06-14 15:32:08: ebpf.plugin ERROR : EBPF PROCESS : Cannot load program: /usr/libexec/netdata/plugins.d/pnetdata_ebpf_process.3.10.0.o (errno 13, Permission denied)
2020-06-14 15:32:19: netdata ERROR : PLUGINSD[ebpf] : read failed: end of file (errno 9, Bad file descriptor)

You can also check for errors related to ebpf.plugin inside /var/log/audit/audit.log:

type=AVC msg=audit(1586260134.952:97): avc:  denied  { map_create } for  pid=1387 comm="ebpf.pl" scontext=system_u:system_r:unconfined_service_t:s0 tcontext=system_u:system_r:unconfined_service_t:s0 tclass=bpf permissive=0
type=SYSCALL msg=audit(1586260134.952:97): arch=c000003e syscall=321 success=no exit=-13 a0=0 a1=7ffe6b36f000 a2=70 a3=0 items=0 ppid=1135 pid=1387 auid=4294967295 uid=994 gid=990 euid=0 suid=0 fsuid=0 egid=990 sgid=990 fsgid=990 tty=(none) ses=4294967295 comm="ebpf_proc
ess.pl" exe="/usr/libexec/netdata/plugins.d/ebpf.plugin" subj=system_u:system_r:unconfined_service_t:s0 key=(null)

If you see similar errors, you will have to adjust SELinux's policies to enable the eBPF collector.

Creation of bpf policies

To enable ebpf.plugin to run on a distribution with SELinux enabled, it will be necessary to take the following actions.

First, stop the Netdata Agent.

# systemctl stop netdata

Next, create a policy with the audit.log file you examined earlier.

# grep ebpf.plugin /var/log/audit/audit.log | audit2allow -M netdata_ebpf

This will create two new files: netdata_ebpf.te and netdata_ebpf.mod.

Edit the netdata_ebpf.te file to change the options class and allow. You should have the following at the end of the netdata_ebpf.te file.

module netdata_ebpf 1.0;
require {
        type unconfined_service_t;
        class bpf { map_create map_read map_write prog_load prog_run };
}
#============= unconfined_service_t ==============
allow unconfined_service_t self:bpf { map_create map_read map_write prog_load prog_run };

Then compile your netdata_ebpf.te file with the following commands to create a binary that loads the new policies:

# checkmodule -M -m -o netdata_ebpf.mod netdata_ebpf.te 
# semodule_package -o netdata_ebpf.pp -m netdata_ebpf.mod

Finally, you can load the new policy and start the Netdata agent again:

# semodule -i netdata_ebpf.pp
# systemctl start netdata

Lockdown

Beginning with version 5.4, the Linux kernel has a feature called "lockdown," which may affect ebpf.plugin depending how the kernel was compiled. The following table shows how the lockdown module impacts ebpf.plugin based on the selected options:

Enforcing kernel lockdown Enable lockdown LSM early in init Default lockdown mode Can ebpf.plugin run with this?
YES NO NO YES
YES Yes None YES
YES Yes Integrity YES
YES Yes Confidentiality NO

If you or your distribution compiled the kernel with the last combination, your system cannot load shared libraries required to run ebpf.plugin.

Cleaning kprobe_events

The eBPF collector adds entries to the file /sys/kernel/debug/tracing/kprobe_events, and cleans them on exit, unless another process prevents it. If you need to clean the eBPF entries safely, you can manually run the script /usr/libexec/netdata/plugins.d/reset_netdata_trace.sh.

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