How eBPF Works
AdvancedeBPF lets you run small, sandboxed programs inside the Linux kernel without changing kernel source or loading risky kernel modules. You attach an eBPF program to a hook — a network packet arriving, a system call, a function entry — and it runs safely in kernel space with near-native speed. A verifier proves each program is safe before it runs, and maps let it share data with user space. eBPF has become the foundation for a new generation of observability, networking, and security tools.
Think of trusted inspectors placed inside a factory
Normally, to change how a factory (the kernel) behaves, you would rebuild the machinery (recompile the kernel) or bolt on custom parts that might break everything (a kernel module). eBPF is like being allowed to place small, pre-vetted inspectors at key points on the line — the loading dock, the packing station, the exit. Before any inspector is allowed in, a strict safety officer (the verifier) checks they cannot jam the machines. They observe and can even redirect items, at full line speed, without ever stopping the factory.
Step by Step
Key Concepts
The Verifier
The kernel component that statically checks every eBPF program before it runs, guaranteeing it terminates and cannot corrupt memory or crash the kernel. It is what makes running kernel code safe.
Hooks
The attachment points where eBPF programs run — network packet processing (XDP/tc), system calls, tracepoints, and kprobes/uprobes on kernel or user functions. The hook determines when your program executes.
Maps
Efficient key-value data structures shared between the in-kernel eBPF program and user-space applications, used to store state, collect metrics, and pass data across the boundary.
eBPF vs Kernel Modules
A kernel module runs unrestricted and can crash the system; an eBPF program is sandboxed, verified, and portable. eBPF delivers much of the power with far less risk and no recompilation.
Key Facts
- eBPF runs sandboxed, verified programs in the kernel at near-native speed — extending the kernel without recompiling it or risking a crash from a module.
- It underpins modern tooling: Cilium (networking and service mesh), Falco (security), and many observability tools use eBPF to see and shape system behaviour with low overhead.
- Because programs run in the kernel data path, eBPF can observe and act on every packet or syscall efficiently — impossible for user-space tools without heavy overhead.
Real-World Applications
High-performance networking
Cilium uses eBPF to route, load-balance, and enforce network policy for Kubernetes pods directly in the kernel, replacing slower iptables-based approaches and even implementing a service mesh without sidecars.
Deep observability and security
eBPF programs trace syscalls and function calls to produce detailed metrics and detect suspicious behaviour (like Falco) with minimal overhead, seeing far more than user-space agents can.
Frequently Asked Questions
What is eBPF?
eBPF (extended Berkeley Packet Filter) is a technology that lets you run small, sandboxed programs inside the Linux kernel in response to events — a network packet arriving, a system call, a function being called — without modifying kernel source or loading a kernel module. The programs run safely at near-native speed and can observe or change system behaviour, which is why eBPF has become the foundation for modern networking, observability, and security tools.
How does eBPF stay safe when running in the kernel?
Before any eBPF program is loaded, the kernel verifier statically analyses it to prove it is safe — that it will always terminate (no unbounded loops), only accesses valid memory, and cannot crash the kernel. Only programs that pass verification are allowed to run, and they are then JIT-compiled to native machine code. This sandboxing is what makes running custom code in the kernel practical without the risk of a traditional kernel module.
What is the difference between eBPF and a kernel module?
A kernel module runs with full, unrestricted kernel privileges — extremely powerful, but a bug can crash or compromise the entire system, and it often requires matching the exact kernel version. An eBPF program is sandboxed and verified for safety, JIT-compiled for speed, and more portable across kernel versions. eBPF gives much of the power of kernel-level code with far less risk and without recompiling the kernel.
What is eBPF used for?
eBPF powers a new generation of infrastructure tooling. In networking, projects like Cilium use it for fast packet processing, load balancing, network policy, and even service meshes without sidecars. In observability, eBPF traces syscalls and functions to produce rich metrics and traces with low overhead. In security, tools like Falco use it to detect suspicious runtime behaviour. Its ability to run efficiently in the kernel data path is what makes all of these possible.