Strace Ltrace

mohitmishra786/low-level-dev-skills/skills/profilers/strace-ltrace

作者 mohitmishra786bdc58472fa9f无许可证253 个星标收录于 2026年10月9日更新于 2026年10月9日仓库3个月前更新

strace and ltrace skill for system call and library call tracing. Use when a binary behaves incorrectly without crashing, diagnosing file-not-found errors, permission failures, network issues, or unexpected library calls by tracing syscalls and library function calls. Activates on queries about strace, ltrace, syscall tracing, library interception, ENOENT, EPERM, strace -e, or diagnosing binary behaviour without a debugger.

仅含说明Software Development

AI 生成的概览

指导代理使用 strace 和 ltrace 跟踪系统调用与库调用，以诊断行为异常的程序。

功能: 该技能提供使用 strace 跟踪系统调用、使用 ltrace 跟踪用户空间库调用的操作指引。内容涵盖基本跟踪与附加到进程、按系统调用类别过滤、ENOENT 和 EPERM 等常见错误码、常用参数，以及针对文件缺失、权限、网络连接、库加载和 seccomp 终止的实用诊断流程。产出为命令示例与结果解读说明，而非脚本。
适用场景: 适用于程序未崩溃但行为异常，或需要查明程序访问了哪些文件、网络连接或库函数的情况。也适合诊断文件未找到、权限不足和动态库加载失败等问题。
运行要求: 需要在 Linux 系统上安装 strace 和 ltrace，并具备跟踪进程的权限（通常为 root 或 ptrace 能力）。该技能不附带脚本，仅引用一份模式参考文档。

strace / ltrace

Purpose

Guide agents through tracing system calls with strace and library calls with ltrace — the most effective tools for diagnosing incorrect binary behaviour without a crash or debugger.

Triggers

"My program behaves incorrectly — how do I trace what it's doing?"
"How do I find what files a binary is opening?"
"strace shows ENOENT — how do I interpret it?"
"How do I trace network calls with strace?"
"What is ltrace and how does it differ from strace?"
"How do I trace a running process?"

Workflow

1. Basic strace usage

bash

# Trace all syscalls of a commandstrace ./myapp arg1 arg2
# Attach to running processstrace -p 12345
# Trace child processes too (-f = follow fork)strace -f ./myapp
# Save to file (raw output — not stdout)strace ./myapp 2> trace.txt
# Most useful: timestamps + summarystrace -t -f ./myapp 2>&1 | head -100

# Trace all syscalls of a commandstrace ./myapp arg1 arg2
# Attach to running processstrace -p 12345
# Trace child processes too (-f = follow fork)strace -f ./myapp
# Save to file (raw output — not stdout)strace ./myapp 2> trace.txt
# Most useful: timestamps + summarystrace -t -f ./myapp 2>&1 | head -100

2. Filter by syscall category

bash

# Trace file operations onlystrace -e trace=file ./myapp
# Trace network syscallsstrace -e trace=network ./myapp
# Trace specific syscallsstrace -e trace=open,openat,read,write ./myapp
# Trace process managementstrace -e trace=process ./myapp
# Trace memory operationsstrace -e trace=memory ./myapp
# Trace signalsstrace -e trace=signal ./myapp
# Multiple categoriesstrace -e trace=file,network ./myapp

# Trace file operations onlystrace -e trace=file ./myapp
# Trace network syscallsstrace -e trace=network ./myapp
# Trace specific syscallsstrace -e trace=open,openat,read,write ./myapp
# Trace process managementstrace -e trace=process ./myapp
# Trace memory operationsstrace -e trace=memory ./myapp
# Trace signalsstrace -e trace=signal ./myapp
# Multiple categoriesstrace -e trace=file,network ./myapp

Category	Syscalls included
`file`	open, openat, stat, access, unlink, rename, ...
`network`	socket, connect, bind, accept, send, recv, ...
`process`	fork, exec, wait, clone, exit, ...
`memory`	mmap, munmap, mprotect, brk, ...
`signal`	kill, sigaction, sigprocmask, ...
`ipc`	pipe, socket pair, shmget, ...
`desc`	close, dup, poll, select, epoll, ...

3. Interpreting common errors

bash

# See return values and errorsstrace -e trace=file ./myapp 2>&1 | grep -E "ENOENT|EPERM|EACCES|ENOTSUP"

# See return values and errorsstrace -e trace=file ./myapp 2>&1 | grep -E "ENOENT|EPERM|EACCES|ENOTSUP"

Error	Meaning	Common cause
`ENOENT`	No such file or directory	Config file missing, wrong path
`EACCES`	Permission denied	File permissions, SELinux
`EPERM`	Operation not permitted	Missing capability, suid needed
`EADDRINUSE`	Address already in use	Port already bound
`ETIMEDOUT`	Connection timed out	Network unreachable, firewall
`ECONNREFUSED`	Connection refused	Server not listening
`EAGAIN`	Resource temporarily unavailable	Non-blocking I/O, try again
`ENOMEM`	Out of memory	Allocation failed
`EBADF`	Bad file descriptor	Using closed/invalid fd
`ENOEXEC`	Exec format error	Wrong binary format for arch

bash

# Find what file is not foundstrace ./myapp 2>&1 | grep 'ENOENT'# Example output:# openat(AT_FDCWD, "/etc/myapp.conf", O_RDONLY) = -1 ENOENT (No such file or directory)# → Config file expected at /etc/myapp.conf

# Find what file is not foundstrace ./myapp 2>&1 | grep 'ENOENT'# Example output:# openat(AT_FDCWD, "/etc/myapp.conf", O_RDONLY) = -1 ENOENT (No such file or directory)# → Config file expected at /etc/myapp.conf

4. Useful strace flags

bash

# Show strings fully (default truncates at 32 chars)strace -s 256 ./myapp
# Timestampsstrace -t ./myapp     # wall clock timestrace -T ./myapp     # time spent in each syscallstrace -r ./myapp     # relative timestamps
# System call count summarystrace -c ./myapp# Shows count, time, errors per syscall — great for profiling
# Trace with PIDs in output (for -f)strace -f -p ./myapp# Output: [pid 12346] open("/etc/passwd", O_RDONLY) = 3
# Decode numerical argumentsstrace -e verbose=all ./myapp
# Print instruction pointer at each syscallstrace -i ./myapp

# Show strings fully (default truncates at 32 chars)strace -s 256 ./myapp
# Timestampsstrace -t ./myapp     # wall clock timestrace -T ./myapp     # time spent in each syscallstrace -r ./myapp     # relative timestamps
# System call count summarystrace -c ./myapp# Shows count, time, errors per syscall — great for profiling
# Trace with PIDs in output (for -f)strace -f -p ./myapp# Output: [pid 12346] open("/etc/passwd", O_RDONLY) = 3
# Decode numerical argumentsstrace -e verbose=all ./myapp
# Print instruction pointer at each syscallstrace -i ./myapp

5. ltrace — library call tracing

bash

# Trace all library callsltrace ./myapp
# Trace specific library functionltrace -e malloc,free,fopen ./myapp
# Trace nested calls (lib → lib)ltrace -n 2 ./myapp   # indent nested calls
# Trace with syscalls tooltrace -S ./myapp
# Attach to running processltrace -p 12345
# Summary statisticsltrace -c ./myapp

# Trace all library callsltrace ./myapp
# Trace specific library functionltrace -e malloc,free,fopen ./myapp
# Trace nested calls (lib → lib)ltrace -n 2 ./myapp   # indent nested calls
# Trace with syscalls tooltrace -S ./myapp
# Attach to running processltrace -p 12345
# Summary statisticsltrace -c ./myapp

Typical ltrace output:

strace vs ltrace:

	strace	ltrace
Traces	Kernel syscalls	User-space library calls
Overhead	Lower	Higher (PLT hooking)
Shows	`open()`, `read()`, `write()`	`fopen()`, `malloc()`, `printf()`
Use when	Binary interacts with OS/files/network	Binary calls library functions you can't see

6. Practical diagnosis workflows

bash

# Find missing config filestrace -e trace=openat,open ./myapp 2>&1 | grep ENOENT
# Find what network connections are madestrace -e trace=network -f ./myapp 2>&1 | grep connect
# Debug dynamic library loading failuresstrace -e trace=openat ./myapp 2>&1 | grep "\.so"
# Find permission issuesstrace -e trace=file ./myapp 2>&1 | grep -E "EACCES|EPERM"
# Debug slow startup (find where time is spent)strace -c ./myapp 2>&1# Look for high % time in unexpected syscalls
# Watch IPC/shared memorystrace -e trace=ipc,shm ./myapp
# Find what the binary exec'sstrace -e trace=execve -f ./myapp

# Find missing config filestrace -e trace=openat,open ./myapp 2>&1 | grep ENOENT
# Find what network connections are madestrace -e trace=network -f ./myapp 2>&1 | grep connect
# Debug dynamic library loading failuresstrace -e trace=openat ./myapp 2>&1 | grep "\.so"
# Find permission issuesstrace -e trace=file ./myapp 2>&1 | grep -E "EACCES|EPERM"
# Debug slow startup (find where time is spent)strace -c ./myapp 2>&1# Look for high % time in unexpected syscalls
# Watch IPC/shared memorystrace -e trace=ipc,shm ./myapp
# Find what the binary exec'sstrace -e trace=execve -f ./myapp

7. seccomp filter debugging

If a program is killed by a seccomp policy, strace reveals which syscall triggered it:

For strace output patterns and ltrace filtering examples, see references/strace-patterns.md [blocked].

Related skills

Use skills/debuggers/gdb when strace shows the failing location and you need to inspect internals
Use skills/binaries/elf-inspection to understand what libraries and symbols a binary uses
Use skills/binaries/dynamic-linking for diagnosing LD_* and library loading issues
Use skills/profilers/linux-perf for performance profiling (strace overhead is too high for perf)

来源与署名

来源：mohitmishra786/low-level-dev-skills位于skills/profilers/strace-ltrace提交bdc5847

许可证：无许可证

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Strace Ltrace

strace / ltrace

Purpose

Triggers

Workflow

1. Basic strace usage

2. Filter by syscall category

3. Interpreting common errors

4. Useful strace flags

5. ltrace — library call tracing

6. Practical diagnosis workflows

7. seccomp filter debugging

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