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strace-ltrace

Use when a binary misbehaves without crashing and the question is which file, socket, syscall, or library call fails: strace for syscalls, ltrace for library calls. Not for stepping: use gdb.

.devin/skills/strace-ltrace/SKILL.md

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Apache-2.0

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# strace and ltrace

`strace` (6.19 on the grounding host) prints every system call a process makes with its arguments, return value, and errno. `ltrace` (0.7.91) does the same for calls that go through PLT slots into shared libraries. Together they answer "what did the program ask the system for, and what did it get back" without a debugger or a rebuild, which is the fastest route to a missing file, a refused connection, or a permission error.

## Contract

| Field | Bound contract |
|---|---|
| Trigger | A program exits wrong, hangs, cannot find a file, cannot connect, is killed by a policy, or starts slowly, and the user wants to see its syscalls or library calls. |
| Authority | Reversible local: writes only trace output files named with `-o` in the working directory; rollback is deleting them. Attaching to a running process needs ptrace permission and is proposed, not forced. No remote mutation. |
| Side effect | The traced program runs slower: every traced syscall stops the process twice. `ltrace` costs more than `strace` because it breakpoints PLT entries. |
| Done | The failing call is named with its arguments, return value, and errno, and the report states the cause (missing path, wrong permission, closed descriptor, refused address) and the fix. |

## Inputs