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# eBPF monitoring with Netdata

eBPF consists of a wide toolchain that ultimately outputs a set of bytecode that will run inside the eBPF virtual
machine (VM) which lives inside the Linux kernel. The program in particular is executed in response to a [tracepoint
or kprobe](#probes-and-tracepoints) activation.

Netdata has written many eBPF programs, which, when compiled and integrated into the Netdata Agent, are able to collect
a wide array of data about the host that would otherwise be impossible. The data eBPF programs can collect is truly unique,
which gives the Netdata Agent access to data that is high value but normally hard to capture.

eBPF monitoring can help you troubleshoot and debug how applications interact with the Linux kernel. See
our [guide on troubleshooting apps with eBPF metrics](/docs/guides/troubleshoot/monitor-debug-applications-ebpf.md) for
configuration and troubleshooting tips.

<figure>
  <img src="https://user-images.githubusercontent.com/1153921/74746434-ad6a1e00-5222-11ea-858a-a7882617ae02.png" alt="An example of VFS charts, made possible by the eBPF collector plugin" />
  <figcaption>An example of VFS charts made possible by the eBPF collector plugin.</figcaption>
</figure>

## Probes and Tracepoints

The following two features from the Linux kernel are used by Netdata to run eBPF programs:

- Kprobes and return probes (kretprobe): Probes can insert virtually into any kernel instruction. When eBPF runs in
  `entry` mode, it attaches only `kprobes` for internal functions monitoring calls and some arguments every time a
  function is called. The user can also change configuration to use [`return`](#global) mode, and this will allow users
  to monitor return from these functions and detect possible failures.
- Tracepoints are hooks to call specific functions. Tracepoints are more stable than `kprobes` and are preferred when
  both options are available.

In each case, wherever a normal kprobe, kretprobe, or tracepoint would have run its hook function, an eBPF program is
run instead, performing various collection logic before letting the kernel continue its normal control flow.

There are more methods by which eBPF programs can be triggered but which are not currently supported, such as via uprobes
which allow hooking into arbitrary user-space functions in a similar manner to kprobes.

## Manually 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](/packaging/installer/methods/kickstart.md#static-builds) for kernels older
than `4.11`, 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](#configuration)
section for details.

## Charts

The eBPF collector creates charts on different menus, like System Overview, Memory, MD arrays, Disks, Filesystem,
Mount Points, Networking Stack, systemd Services, and Applications.

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.

### System overview

Not all charts within the System Overview menu are enabled by default, because they add around 100ns overhead for each
function call, this number is small for a human perspective, but the functions are called many times creating an impact
on host. See the [configuration](#configuration) section for details about how to enable them.

#### Processes

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)`. To generate this chart, the eBPF
collector uses the following `tracepoints` and `kprobe`:

- `sched/sched_process_fork`: Tracepoint called after a call for `fork (2)`, `vfork (2)` and `clone (2)`.
- `sched/sched_process_exec`: Tracepoint called after a exec-family syscall.
- `kprobe/kernel_clone`: This is the main [`fork()`](https://elixir.bootlin.com/linux/v5.10/source/kernel/fork.c#L2415)
   routine since kernel `5.10.0` was released.
- `kprobe/_do_fork`: Like `kernel_clone`, but this was the main function between kernels `4.2.0` and `5.9.16`
- `kprobe/do_fork`: This was the main function before kernel `4.2.0`.

#### Process 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](https://en.wikipedia.org/wiki/Zombie_process). To get the metrics, the collector uses:

- `sched/sched_process_exit`: Tracepoint called after a task exits.
- `kprobe/release_task`: This function is called when a process exits, as the kernel still needs to remove the process
  descriptor.

#### Task error

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

#### Swap

Inside the swap submenu the eBPF plugin creates the chart `swapcalls`; this chart is displaying when processes are
calling functions [`swap_readpage` and `swap_writepage`](https://hzliu123.github.io/linux-kernel/Page%20Cache%20in%20Linux%202.6.pdf ),
which are functions responsible for doing IO in swap memory. To collect the exact moment that an access to swap happens,
the collector attaches `kprobes` for cited functions.

#### Soft IRQ

The following `tracepoints` are used to measure time usage for soft IRQs:

- [`irq/softirq_entry`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_softirq_entry): Called
   before softirq handler
- [`irq/softirq_exit`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_softirq_exit): Called when
   softirq handler returns.

#### Hard IRQ

The following tracepoints are used to measure the latency of servicing a
hardware interrupt request (hard IRQ).

- [`irq/irq_handler_entry`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_irq_handler_entry):
  Called immediately before the IRQ action handler.
- [`irq/irq_handler_exit`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_irq_handler_exit):
  Called immediately after the IRQ action handler returns.
- `irq_vectors`: These are traces from `irq_handler_entry` and
  `irq_handler_exit` when an IRQ is handled. The following elements from vector
  are triggered:
    - `irq_vectors/local_timer_entry`
    - `irq_vectors/local_timer_exit`
    - `irq_vectors/reschedule_entry`
    - `irq_vectors/reschedule_exit`
    - `irq_vectors/call_function_entry`
    - `irq_vectors/call_function_exit`
    - `irq_vectors/call_function_single_entry`
    - `irq_vectors/call_function_single_xit`
    - `irq_vectors/irq_work_entry`
    - `irq_vectors/irq_work_exit`
    - `irq_vectors/error_apic_entry`
    - `irq_vectors/error_apic_exit`
    - `irq_vectors/thermal_apic_entry`
    - `irq_vectors/thermal_apic_exit`
    - `irq_vectors/threshold_apic_entry`
    - `irq_vectors/threshold_apic_exit`
    - `irq_vectors/deferred_error_entry`
    - `irq_vectors/deferred_error_exit`
    - `irq_vectors/spurious_apic_entry`
    - `irq_vectors/spurious_apic_exit`
    - `irq_vectors/x86_platform_ipi_entry`
    - `irq_vectors/x86_platform_ipi_exit`

#### IPC shared memory

To monitor shared memory system call counts, the following `kprobes` are used:

- `shmget`: Runs when [`shmget`](https://man7.org/linux/man-pages/man2/shmget.2.html) is called.
- `shmat`: Runs when [`shmat`](https://man7.org/linux/man-pages/man2/shmat.2.html) is called.
- `shmdt`: Runs when [`shmdt`](https://man7.org/linux/man-pages/man2/shmat.2.html) is called.
- `shmctl`: Runs when [`shmctl`](https://man7.org/linux/man-pages/man2/shmctl.2.html) is called.

### Memory

In the memory submenu the eBPF plugin creates two submenus **page cache** and **synchronization** with the following
organization:

* Page Cache
    * Page cache ratio
    * Dirty pages
    * Page cache hits
    * Page cache misses
* Synchronization
    * File sync
    * Memory map sync
    * File system sync
    * File range sync

#### Page cache ratio

The chart `cachestat_ratio` shows how processes are accessing page cache. In a normal scenario, we expect values around
100%, which means that the majority of the work on the machine is processed in memory. To calculate the ratio, Netdata
attaches `kprobes` for kernel functions:

- `add_to_page_cache_lru`: Page addition.
- `mark_page_accessed`: Access to cache.
- `account_page_dirtied`: Dirty (modified) pages.
- `mark_buffer_dirty`: Writes to page cache.

#### Dirty pages

On `cachestat_dirties` Netdata demonstrates the number of pages that were modified. This chart shows the number of calls
to the function `mark_buffer_dirty`.

#### Page cache hits

A page cache hit is when the page cache is successfully accessed with a read operation. We do not count pages that were
added relatively recently.

#### Page cache misses

A page cache miss means that a page was not inside memory when the process tried to access it. This chart shows the
result of the difference for calls between functions `add_to_page_cache_lru` and `account_page_dirtied`.

#### File sync

This chart shows calls to synchronization methods, [`fsync(2)`](https://man7.org/linux/man-pages/man2/fdatasync.2.html)
and [`fdatasync(2)`](https://man7.org/linux/man-pages/man2/fdatasync.2.html), to transfer all modified page caches
for the files on disk devices. These calls block until the disk reports that the transfer has been completed. They flush
data for specific file descriptors.

#### Memory map sync

The chart shows calls to [`msync(2)`](https://man7.org/linux/man-pages/man2/msync.2.html) syscalls. This syscall flushes
changes to a file that was mapped into memory using [`mmap(2)`](https://man7.org/linux/man-pages/man2/mmap.2.html).

#### File system sync

This chart monitors calls demonstrating commits from filesystem caches to disk. Netdata attaches `kprobes` for
[`sync(2)`](https://man7.org/linux/man-pages/man2/sync.2.html), and [`syncfs(2)`](https://man7.org/linux/man-pages/man2/sync.2.html).

#### File range sync

This chart shows calls to [`sync_file_range(2)`](https://man7.org/linux/man-pages/man2/sync_file_range.2.html) which
synchronizes file segments with disk.

> Note: This is the most dangerous syscall to synchronize data, according to its manual.

### Multiple Device (MD) arrays

The eBPF plugin shows multi-device flushes happening in real time. This can be used to explain some spikes happening
in [disk latency](#disk) charts.

By default, MD flush is disabled. To enable it, configure your
`/etc/netdata/ebpf.d.conf` file as:

```conf
[global]
    mdflush = yes
```

#### MD flush

To collect data related to Linux multi-device (MD) flushing, the following kprobe is used:

-  `kprobe/md_flush_request`: called whenever a request for flushing multi-device data is made.

### Disk

The eBPF plugin also shows a chart in the Disk section when the `disk` thread is enabled. This will create the
chart `disk_latency_io` for each disk on the host. The following tracepoints are used:

- [`block/block_rq_issue`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_block_rq_issue):
  IO request operation to a device drive.
- [`block/block_rq_complete`](https://www.kernel.org/doc/html/latest/core-api/tracepoint.html#c.trace_block_rq_complete):
  IO operation completed by device.

### Filesystem

This group has charts demonstrating how applications interact with the Linux
kernel to open and close file descriptors. It also brings latency charts for
several different filesystems.

#### ext4

To measure the latency of executing some actions in an
[ext4](https://elixir.bootlin.com/linux/latest/source/fs/ext4) filesystem, the
collector needs to attach `kprobes` and `kretprobes` for each of the following
functions:

- `ext4_file_read_iter`: Function used to measure read latency.
- `ext4_file_write_iter`: Function used to measure write latency.
- `ext4_file_open`: Function used to measure open latency.
- `ext4_sync_file`: Function used to measure sync latency.

#### ZFS

To measure the latency of executing some actions in a zfs filesystem, the
collector needs to attach `kprobes` and `kretprobes` for each of the following
functions:

- `zpl_iter_read`: Function used to measure read latency.
- `zpl_iter_write`: Function used to measure write latency.
- `zpl_open`: Function used to measure open latency.
- `zpl_fsync`: Function used to measure sync latency.

#### XFS

To measure the latency of executing some actions in an
[xfs](https://elixir.bootlin.com/linux/latest/source/fs/xfs) filesystem, the
collector needs to attach `kprobes` and `kretprobes` for each of the following
functions:

- `xfs_file_read_iter`: Function used to measure read latency.
- `xfs_file_write_iter`: Function used to measure write latency.
- `xfs_file_open`: Function used to measure open latency.
- `xfs_file_fsync`: Function used to measure sync latency.

#### NFS

To measure the latency of executing some actions in an
[nfs](https://elixir.bootlin.com/linux/latest/source/fs/nfs) filesystem, the
collector needs to attach `kprobes` and `kretprobes` for each of the following
functions:

- `nfs_file_read`: Function used to measure read latency.
- `nfs_file_write`: Function used to measure write latency.
- `nfs_file_open`: Functions used to measure open latency.
- `nfs4_file_open`: Functions used to measure open latency for NFS v4.
- `nfs_getattr`: Function used to measure sync latency.

#### btrfs

To measure the latency of executing some actions in a [btrfs](https://elixir.bootlin.com/linux/latest/source/fs/btrfs/file.c)
filesystem, the collector needs to attach `kprobes` and `kretprobes` for each of the following functions:

> Note: We are listing two functions used to measure `read` latency, but we use either `btrfs_file_read_iter` or
`generic_file_read_iter`, depending on kernel version.

- `btrfs_file_read_iter`: Function used to measure read latency since kernel `5.10.0`.
- `generic_file_read_iter`: Like `btrfs_file_read_iter`, but this function was used before kernel `5.10.0`.
- `btrfs_file_write_iter`: Function used to write data.
- `btrfs_file_open`: Function used to open files.
- `btrfs_sync_file`: Function used to synchronize data to filesystem.

#### File descriptor

To give metrics related to `open` and `close` events, instead of attaching kprobes for each syscall used to do these
events, the collector attaches `kprobes` for the common function used for syscalls:

- [`do_sys_open`](https://0xax.gitbooks.io/linux-insides/content/SysCall/linux-syscall-5.html ): Internal function used to
   open files.
- [`do_sys_openat2`](https://elixir.bootlin.com/linux/v5.6/source/fs/open.c#L1162):
  Function called from `do_sys_open` since version `5.6.0`.
- [`close_fd`](https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2271761.html): Function used to close file
  descriptor since kernel `5.11.0`.
- `__close_fd`: Function used to close files before version `5.11.0`.

#### File error

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

#### VFS

The Linux Virtual File System (VFS) is an abstraction layer on top of a
concrete filesystem like the ones listed in the parent section, e.g. `ext4`.

In this section we list the mechanism by which we gather VFS data, and what
charts are consequently created.

##### VFS eBPF Hooks

To measure the latency and total quantity of executing some VFS-level
functions, ebpf.plugin needs to attach kprobes and kretprobes for each of the
following functions:

- `vfs_write`: Function used monitoring the number of successful & failed
  filesystem write calls, as well as the total number of written bytes.
- `vfs_writev`: Same function as `vfs_write` but for vector writes (i.e. a
  single write operation using a group of buffers rather than 1).
- `vfs_read`: Function used for monitoring the number of successful & failed
  filesystem read calls, as well as the total number of read bytes.
- `vfs_readv` Same function as `vfs_read` but for vector reads (i.e. a single
  read operation using a group of buffers rather than 1).
- `vfs_unlink`: Function used for monitoring the number of successful & failed
  filesystem unlink calls.
- `vfs_fsync`: Function used for monitoring the number of successful & failed
  filesystem fsync calls.
- `vfs_open`: Function used for monitoring the number of successful & failed
  filesystem open calls.
- `vfs_create`: Function used for monitoring the number of successful & failed
  filesystem create calls.

##### VFS Deleted objects

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

##### VFS IO

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

##### VFS IO bytes

This chart also monitors `vfs_read` and `vfs_write` but, instead of the number of calls, it shows the total amount 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.

##### VFS IO errors

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

##### VFS Create

This chart shows the number of calls to `vfs_create`. This function is responsible for creating files.

##### VFS Synchronization

This chart shows the number of calls to `vfs_fsync`. This function is responsible for calling `fsync(2)` or
`fdatasync(2)` on a file. You can see more details in the Synchronization section.

##### VFS Open

This chart shows the number of calls to `vfs_open`. This function is responsible for opening files.

#### Directory Cache

Metrics for directory cache are collected using kprobe for `lookup_fast`, because we are interested in the number of
times this function is accessed. On the other hand, for `d_lookup` we are not only interested in the number of times it
is accessed, but also in possible errors, so we need to attach a `kretprobe`. For this reason, the following is used:

- [`lookup_fast`](https://lwn.net/Articles/649115/): Called to look at data inside the directory cache.
- [`d_lookup`](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/dcache.c?id=052b398a43a7de8c68c13e7fa05d6b3d16ce6801#n2223):
  Called when the desired file is not inside the directory cache.

### Mount Points

The following `kprobes` are used to collect `mount` & `unmount` call counts:

- [`mount`](https://man7.org/linux/man-pages/man2/mount.2.html): mount filesystem on host.
- [`umount`](https://man7.org/linux/man-pages/man2/umount.2.html): umount filesystem on host.

### Networking Stack

Netdata monitors socket bandwidth attaching `kprobes` for internal functions.

#### TCP functions

This chart demonstrates calls to functions `tcp_sendmsg`, `tcp_cleanup_rbuf`, and `tcp_close`; these functions are used
to send & receive data and to close connections when `TCP` protocol is used.

#### TCP bandwidth

Like the previous chart, this one also monitors `tcp_sendmsg` and `tcp_cleanup_rbuf`, but instead of showing the number
of calls, it demonstrates the number of bytes sent and received.

#### TCP retransmit

This chart demonstrates calls to function `tcp_retransmit` that is responsible for executing TCP retransmission when the
receiver did not return the packet during the expected time.

#### UDP functions

This chart demonstrates calls to functions `udp_sendmsg` and `udp_recvmsg`, which are responsible for sending &
receiving data for connections when the `UDP` protocol is used.

#### UDP bandwidth

Like the previous chart, this one also monitors `udp_sendmsg` and `udp_recvmsg`, but instead of showing the number of
calls, it monitors the number of bytes sent and received.

### Apps

#### OOM Killing

These are tracepoints related to [OOM](https://en.wikipedia.org/wiki/Out_of_memory) killing processes.

-  `oom/mark_victim`: Monitors when an oomkill event happens.

## Configuration

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

```bash
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`.

```conf
[plugins]
   ebpf = yes
```

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

```bash
cd /etc/netdata/   # Replace with your Netdata configuration directory, if not /etc/netdata/
./edit-config ebpf.d.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.
- `update every`:  Number of seconds used for eBPF to send data for Netdata.
- `pid table size`: Defines the maximum number of PIDs stored inside the application hash table.

#### Integration with `apps.plugin`

The eBPF collector also creates charts for each running application through an integration with the
[`apps.plugin`](/collectors/apps.plugin/README.md). This integration helps you understand how specific applications
interact with the Linux kernel.

If you want to _disable_ the integration with `apps.plugin` along with the above charts, change the setting `apps` to
`no`.

```conf
[global]
   apps = yes
```

When the integration is enabled, eBPF collector allocates memory for each process running. The total allocated memory
has direct relationship with the kernel version. When the eBPF plugin is running on kernels newer than `4.15`, it uses
per-cpu maps to speed up the update of hash tables. This also implies storing data for the same PID for each processor
it runs.

#### Integration with `cgroups.plugin`

The eBPF collector also creates charts for each cgroup through an integration with the
[`cgroups.plugin`](/collectors/cgroups.plugin/README.md). This integration helps you understand how a specific cgroup
interacts with the Linux kernel.

The integration with `cgroups.plugin` is disabled by default to avoid creating overhead on your system. If you want to
_enable_ the integration with `cgroups.plugin`, change the `cgroups` setting to `yes`.

```conf
[global]
   cgroups = yes
```

If you do not need to monitor specific metrics for your `cgroups`, you can enable `cgroups` inside
`ebpf.d.conf`, and then disable the plugin for a specific `thread` by following the steps in the
[Configuration](#configuration) section.

#### Integration Dashboard Elements

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

> Note: The parenthetical accompanying each bulleted item provides the chart name.

- mem
    - Number of processes killed due out of memory. (`oomkills`)
- process
    - Number of processes created with `do_fork`. (`process_create`)
    - Number of threads created with `do_fork` or `clone (2)`, depending on your system's kernel
      version. (`thread_create`)
    - Number of times that a process called `do_exit`. (`task_exit`)
    - Number of times that a process called `release_task`. (`task_close`)
    - Number of times that an error happened to create thread or process. (`task_error`)
- swap
    - Number of calls to `swap_readpage`. (`swap_read_call`)
    - Number of calls to `swap_writepage`. (`swap_write_call`)
- network
    - Number of bytes sent. (`total_bandwidth_sent`)
    - Number of bytes received. (`total_bandwidth_recv`)
    - Number of calls to `tcp_sendmsg`. (`bandwidth_tcp_send`)
    - Number of calls to `tcp_cleanup_rbuf`. (`bandwidth_tcp_recv`)
    - Number of calls to `tcp_retransmit_skb`. (`bandwidth_tcp_retransmit`)
    - Number of calls to `udp_sendmsg`. (`bandwidth_udp_send`)
    - Number of calls to `udp_recvmsg`. (`bandwidth_udp_recv`)
- file access
    - Number of calls to open files. (`file_open`)
    - Number of calls to open files that returned errors. (`open_error`)
    - Number of files closed. (`file_closed`)
    - Number of calls to close files that returned errors. (`file_error_closed`)
- vfs
    - Number of calls to `vfs_unlink`. (`file_deleted`)
    - Number of calls to `vfs_write`. (`vfs_write_call`)
    - Number of calls to write a file that returned errors. (`vfs_write_error`)
    - Number of calls to `vfs_read`. (`vfs_read_call`)
    - Number of bytes written with `vfs_write`. (`vfs_write_bytes`)
    - Number of bytes read with `vfs_read`. (`vfs_read_bytes`)
    - Number of calls to read a file that returned errors. (`vfs_read_error`)
    - Number of calls to `vfs_fsync`. (`vfs_fsync`)
    - Number of calls to sync file that returned errors. (`vfs_fsync_error`)
    - Number of calls to `vfs_open`. (`vfs_open`)
    - Number of calls to open file that returned errors. (`vfs_open_error`)
    - Number of calls to `vfs_create`. (`vfs_create`)
    - Number of calls to open file that returned errors. (`vfs_create_error`)
- page cache
    - Ratio of pages accessed. (`cachestat_ratio`)
    - Number of modified pages ("dirty"). (`cachestat_dirties`)
    - Number of accessed pages. (`cachestat_hits`)
    - Number of pages brought from disk. (`cachestat_misses`)
- directory cache
    - Ratio of files available in directory cache. (`dc_hit_ratio`)
    - Number of files accessed. (`dc_reference`)
    - Number of files accessed that were not in cache. (`dc_not_cache`)
    - Number of files not found. (`dc_not_found`)
- ipc shm
    - Number of calls to `shm_get`. (`shmget_call`)
    - Number of calls to `shm_at`. (`shmat_call`)
    - Number of calls to `shm_dt`. (`shmdt_call`)
    - Number of calls to `shm_ctl`. (`shmctl_call`)

### `[ebpf programs]`

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

- `fd` :  This eBPF program creates charts that show information about calls to open files.
- `mount`: This eBPF program creates charts that show calls to syscalls mount(2) and umount(2).
- `shm`: This eBPF program creates charts that show calls to syscalls shmget(2), shmat(2), shmdt(2) and shmctl(2).
- `sync`: Monitor calls to syscalls sync(2), fsync(2), fdatasync(2), syncfs(2), msync(2), and sync_file_range(2).
- `network viewer`: This eBPF program creates charts with information about `TCP` and `UDP` functions, including the
  bandwidth consumed by each.
- `vfs`: This eBPF program creates charts that show information about VFS (Virtual File System) functions.
- `process`: This eBPF program creates charts that show information about process life. When in `return` mode, it also
  creates charts showing errors when these operations are executed.
- `hardirq`: This eBPF program creates charts that show information about time spent servicing individual hardware
  interrupt requests (hard IRQs).
- `softirq`: This eBPF program creates charts that show information about time spent servicing individual software
  interrupt requests (soft IRQs).
- `oomkill`: This eBPF program creates a chart that shows OOM kills for all applications recognized via
  the `apps.plugin` integration. Note that this program will show application charts regardless of whether apps
  integration is turned on or off.

You can also enable the following eBPF programs:

- `cachestat`: Netdata's eBPF data collector creates charts about the memory page cache. When the integration with
  [`apps.plugin`](/collectors/apps.plugin/README.md) is enabled, this collector creates charts for the whole host _and_
  for each application.
- `dcstat` : This eBPF program creates charts that show information about file access using directory cache. It appends
  `kprobes` for `lookup_fast()` and `d_lookup()` to identify if files are inside directory cache, outside and files are
  not found.
- `disk` : This eBPF program creates charts that show information about disk latency independent of filesystem.
- `filesystem` : This eBPF program creates charts that show information about some filesystem latency.
- `swap` : This eBPF program creates charts that show information about swap access.
- `mdflush`: This eBPF program creates charts that show information about
  multi-device software flushes.

## Thread configuration

You can configure each thread of the eBPF data collector by editing either the `cachestat.conf`, `process.conf`,
or `network.conf` files. Use [`edit-config`](/docs/configure/nodes.md) from your Netdata config directory:

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

### Configuration files

The following configuration files are available:

- `cachestat.conf`: Configuration for the `cachestat` thread.
- `dcstat.conf`: Configuration for the `dcstat` thread.
- `disk.conf`: Configuration for the `disk` thread.
- `fd.conf`: Configuration for the `file descriptor` thread.
- `filesystem.conf`: Configuration for the `filesystem` thread.
- `hardirq.conf`: Configuration for the `hardirq` thread.
- `process.conf`: Configuration for the `process` thread.
- `network.conf`: Configuration for the `network viewer` thread. This config file overwrites the global options and also
  lets you specify which network the eBPF collector monitors.
- `softirq.conf`: Configuration for the `softirq` thread.
- `sync.conf`: Configuration for the `sync` thread.
- `vfs.conf`: Configuration for the `vfs` thread.

### Network configuration

The network configuration has specific options to configure which network(s) the eBPF collector monitors. These options
are divided in the following sections:

#### `[network connections]`

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

```conf
[network connections]
    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](/libnetdata/simple_pattern/README.md). 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 addresses, but this can
  be changed with the `ips` setting.

By default, Netdata displays up to 500 dimensions on network connection 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 connection 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 connection charts, and thus see the name of the service instead of its port, define it:

```conf
[service name]
    19999 = Netdata
```

### Sync configuration

The sync configuration has specific options to disable monitoring for syscalls, as default option all syscalls are
monitored.

```conf
[syscalls]
    sync = yes
    msync = yes
    fsync = yes
    fdatasync = yes
    syncfs = yes
    sync_file_range = yes
```

### Filesystem configuration

The filesystem configuration has specific options to disable monitoring for filesystems, by default all filesystems are
monitored.

```conf
[filesystem]
    btrfsdist = yes
    ext4dist = yes
    nfsdist = yes
    xfsdist = yes
    zfsdist = yes
```

The ebpf program `nfsdist` monitors only `nfs` mount points.

## Troubleshooting

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

```bash
cd /usr/libexec/netdata/plugins.d/
sudo su -s /bin/bash netdata
./ebpf.plugin
```

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

```bash
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.

```bash
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 kernel
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

- [Ubuntu](https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel)
- [Debian](https://kernel-team.pages.debian.net/kernel-handbook/ch-common-tasks.html#s-common-official)
- [Fedora](https://fedoraproject.org/wiki/Building_a_custom_kernel)
- [CentOS](https://wiki.centos.org/HowTos/Custom_Kernel)
- [Arch Linux](https://wiki.archlinux.org/index.php/Kernel/Traditional_compilation)
- [Slackware](https://docs.slackware.com/howtos:slackware_admin:kernelbuilding)

### 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:

```bash
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](https://www.kernel.org/doc/Documentation/trace/ftrace.txt).

## Performance

eBPF monitoring is complex and produces a large volume of metrics. We've discovered scenarios where the eBPF plugin
significantly increases kernel memory usage by several hundred MB.

If your node is experiencing high memory usage and there is no obvious culprit to be found in the `apps.mem` chart,
consider testing for high kernel memory usage by [disabling eBPF monitoring](#configuration). Next,
[restart Netdata](/docs/configure/start-stop-restart.md) with `sudo systemctl restart netdata` to see if system memory
usage (see the `system.ram` chart) has dropped significantly.

Beginning with `v1.31`, kernel memory usage is configurable via the [`pid table size` setting](#ebpf-load-mode)
in `ebpf.conf`.

## SELinux

When [SELinux](https://www.redhat.com/en/topics/linux/what-is-selinux) is enabled, it may prevent `ebpf.plugin` from
starting correctly. Check the Agent's `error.log` file for errors like the ones below:

```bash
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`:

```bash
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.

```bash
# systemctl stop netdata
```

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

```bash
# 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.

```conf
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:

```bash
# 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:

```bash
# semodule -i netdata_ebpf.pp
# systemctl start netdata
```

## Lockdown

Beginning with [version 5.4](https://www.zdnet.com/article/linux-to-get-kernel-lockdown-feature/), 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`.

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