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Introduction:
System call tracing is a cornerstone of Linux security monitoring, debugging, and malware analysis. Traditional tools like `strace` provide raw syscall data but suffer from performance overhead, lack of live interactivity, and difficult‑to‑parse output. Enter snoop – an eBPF‑based syscall tracer that delivers a live terminal user interface (TUI), intelligent filtering, and human‑readable argument decoding, making real‑time system introspection both powerful and accessible.
Learning Objectives:
- Understand how eBPF enables low‑overhead syscall tracing compared to traditional ptrace‑based tools.
- Install and configure snoop on a Linux system, including verifying kernel eBPF support.
- Use snoop’s live TUI and smart filters to monitor, analyze, and debug system call activity for security and performance tasks.
You Should Know:
- Installing Snoop – eBPF Prerequisites and Build from Source
Snoop leverages eBPF (extended Berkeley Packet Filter), which requires a modern Linux kernel (4.18+ recommended). Follow this step‑by‑step guide to install snoop and verify your environment.
Step 1: Check kernel version and eBPF support
uname -r eBPF requires CONFIG_BPF, CONFIG_BPF_SYSCALL, and BPF file system mounted mount | grep bpf If not mounted, run: sudo mount -t bpf none /sys/fs/bpf/
Step 2: Install development tools and dependencies
Debian/Ubuntu sudo apt update && sudo apt install -y git make gcc libelf-dev linux-headers-$(uname -r) clang llvm RHEL/CentOS/Fedora sudo dnf install -y git make gcc elfutils-libelf-devel kernel-devel clang llvm
Step 3: Clone and build snoop
git clone https://github.com/yourusername/snoop.git Replace with actual repo if different cd snoop make
Step 4: Verify the binary and run a quick test
./snoop --help sudo ./snoop -c "ls /tmp" Trace syscalls during a short command
What this does: The build compiles an eBPF program and a userspace TUI controller. Running `snoop` attaches the BPF program to the raw tracepoint `raw_syscalls:sys_enter` and sys_exit, capturing all system call entries and exits with minimal overhead.
2. Live TUI Navigation – Real‑Time Syscall Monitoring
Unlike strace, snoop provides an interactive terminal interface that updates dynamically. This section explains how to use the TUI to monitor live processes.
Step 1: Start snoop without any target to watch all system calls
sudo ./snoop
You will see a live table showing columns: PID, COMM (command name), SYSCALL (e.g., openat, read, write), RET (return value), and decoded arguments.
Step 2: Keyboard shortcuts in TUI
– `↑` / `↓` – Scroll through entries
– `/` – Filter by syscall name or string in arguments
– `F1` – Toggle help panel
– `q` – Quit
– `Ctrl+R` – Reset all filters
Step 3: Filter by process name or PID
sudo ./snoop --pid 1234 Trace specific PID sudo ./snoop --comm nginx Trace all processes named 'nginx'
Step 4: Limit syscall types
sudo ./snoop --syscalls open,read,write Only show these syscalls
Security angle: During incident response, you can attach snoop to a suspicious daemon and filter for execve, `openat` (with file paths), or `socket` calls to detect lateral movement or data exfiltration attempts.
- Smart Argument Decoding – From Raw Numbers to Human‑Readable Context
One of snoop’s standout features is its ability to decode syscall arguments intelligently. For example, `openat` shows file paths instead of file descriptors; `connect` shows resolved IP addresses and ports.
Step 1: Compare strace output vs snoop
strace on a simple web request strace -e trace=network curl -s https://example.com > /dev/null snoop capturing the same sudo ./snoop --comm curl
Notice how snoop decodes `socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)` and `connect(3, {sa_family=AF_INET, sin_port=htons(443), sin_addr=inet_addr(“93.184.216.34”)}, 16)` directly in the TUI.
Step 2: Enable full path resolution for file operations
sudo ./snoop --resolve-paths
This uses the process’s current working directory to show absolute paths for openat, stat, etc.
Step 3: Decode string arguments for `write` and `ioctl`
Snoop automatically truncates and escapes non‑printable characters, making it easy to spot injected data or leaked secrets. Test by writing a sensitive string:
echo "SECRET_KEY=abc123" > /tmp/test.txt sudo ./snoop --syscalls write --comm echo
The TUI will show the actual string being written.
- Smart Filters – Reducing Noise in High‑Throughput Environments
On a busy server, raw syscall traces produce thousands of events per second. snoop’s filtering capabilities allow you to focus on anomalies.
Step 1: Filter by return value (e.g., failed syscalls)
sudo ./snoop --retval -EAGAIN,-EPERM Show only calls returning EAGAIN or EPERM
Step 2: Filter by argument regex
sudo ./snoop --arg-filter "filename=..so$" Show only file open calls loading shared libraries
Step 3: Combine filters and save to a log file
sudo ./snoop --pid $(pgrep -f mysqld) --syscalls read,write --retval -EPIPE --output snoop.log
This logs only the read/write calls from MySQL that return `EPIPE` (broken pipe) – invaluable for debugging connection drops.
Step 4: Use inverted filters to exclude noise
sudo ./snoop --exclude-syscalls futex,gettimeofday,clock_gettime
- Security Use Cases – Detecting Malicious Activity with Snoop
Snoop is not just a debugging tool – it’s a real‑time detection sensor for Linux workstations and servers.
Scenario A: Detect reverse shells
Monitor for suspicious `socket`, `connect`, and `dup2` syscalls.
sudo ./snoop --syscalls socket,connect,dup2 --comm bash
If an attacker spawns `bash` and redirects stdin/stdout to a network socket, you will see `connect` to an external IP followed by dup2(3, 0), dup2(3, 1), etc.
Scenario B: Catch privilege escalation (setuid executions)
sudo ./snoop --syscalls execve --arg-filter "filename=./bin/(bash|sh|su|sudo)" --resolve-paths
Scenario C: Monitor credential dumping via `/proc`
Attackers often read `/proc/self/mem` or /proc//maps. Use snoop to capture all `openat` calls to /proc.
sudo ./snoop --syscalls openat --arg-filter "filename=^/proc/" --resolve-paths
6. Performance Comparison – eBPF vs ptrace
Understanding why snoop outperforms `strace` is crucial for production environments.
Step 1: Measure overhead using a CPU‑intensive workload
Run a workload with strace time strace -c dd if=/dev/zero of=/dev/null bs=1M count=1000 Run same workload with snoop time sudo ./snoop -c "dd if=/dev/zero of=/dev/null bs=1M count=1000"
Expect snoop to be 5–10x faster because eBPF copies only aggregated data to userspace, whereas `strace` traps every syscall via ptrace, context‑switching for each event.
Step 2: Check eBPF program statistics
sudo bpftool prog list | grep -A 5 snoop sudo cat /sys/kernel/debug/tracing/trace_pipe view raw eBPF events
7. Customizing Snoop with eBPF Extensions (Advanced)
For security engineers who want to go beyond pre‑built filters, snoop’s eBPF source can be modified to collect custom data.
Step 1: Locate the eBPF C code
find /path/to/snoop -name ".bpf.c"
Step 2: Add a new tracepoint, e.g., `security_bprm_check` for binary execution
Modify the code to extract the binary path and user context, then recompile:
make clean && make
Step 3: Load the modified eBPF program manually (without the TUI)
sudo bpftool prog load ./snoop.bpf.o /sys/fs/bpf/snoop_custom sudo bpftool map list
This allows you to pipe data to a SIEM or custom dashboard.
What Undercode Say:
- eBPF is no longer just a networking tool – Snoop demonstrates its power for security observability across all system calls with minimal overhead.
- Live TUI changes the game – Real‑time, interactive filtering makes ad‑hoc investigations as fluid as using
top, not as clunky as `strace` log analysis. - Argument decoding exposes hidden behavior – From file paths to resolved IPs, snoop eliminates the “what does this number mean?” friction.
- Performance matters – In production, you can leave snoop running continuously on critical workloads without the performance penalty of ptrace‑based tracers.
- Smart filters enable proactive detection – Instead of sifting through gigabytes of logs, security teams can set up snoop triggers on anomalous syscall patterns.
Prediction:
As eBPF adoption grows, traditional syscall tracing tools like `strace` and `sysdig` will be rapidly supplanted by lightweight, TUI‑driven eBPF tracers like snoop. Within two years, we expect to see snoop integrated into mainstream Linux distributions and default incident response toolkits. Its ability to combine real‑time visibility with low overhead will push security monitoring from “forensics after the fact” to “live detection and containment.” Moreover, as snoop matures, we anticipate plugins for automatic threat hunting rules (e.g., detecting `execve` on temp files followed by connect), making it a staple in both blue team and purple team exercises. The only limitation today is the learning curve for eBPF customization – but once that barrier falls, snoop will become the `tcpdump` of system call analysis.
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Reported By: Syed Muneeb – Hackers Feeds
Extra Hub: Undercode MoN
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