feat(uname): implement uname builtin (Linux only, proc-based) by matt-dz · Pull Request #146 · DataDog/rshell

matt-dz · 2026-03-25T19:45:32Z

Summary

New uname builtin that reads system information from /proc/sys/kernel/ pseudo-files
Linux only — returns exit 1 with "not supported" message on other platforms
Proc path configurable via --proc-path / interp.ProcPath() (supports /host/proc for containers)
Adds ProcPath() accessor to ProcProvider

Flags (POSIX)

Flag	Source	Description
`-s`	`sys/kernel/ostype`	Kernel name (default)
`-n`	`sys/kernel/hostname`	Network node hostname
`-r`	`sys/kernel/osrelease`	Kernel release
`-v`	`sys/kernel/version`	Kernel version
`-m`	`sys/kernel/arch`	Machine hardware name
`-a`	all of the above	Print all info
`-h`	—	Help

Test plan

14 Go tests with fake proc tree covering every flag, combined flags, errors, custom proc path
go test ./builtins/tests/uname/... passes
go test ./allowedsymbols/... passes
go test ./... full suite passes
CI passes

🤖 Generated with Claude Code

Add uname command that reads system information from /proc/sys/kernel/ pseudo-files. Supports POSIX flags: -s (kernel name, default), -n (hostname), -r (release), -v (version), -m (machine), -a (all). The proc path is configurable via --proc-path / interp.ProcPath(), supporting containerized environments where /proc is mounted at /host/proc or similar. Adds ProcPath() accessor to ProcProvider so builtins can construct proc file paths from the configured base path. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Move proc file reading into ProcProvider.ReadKernelFile(), following the same pattern as ps which delegates to procinfo. The uname builtin now has zero direct os package usage — all proc I/O goes through the ProcProvider abstraction. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Previously showed a confusing "cannot read ostype: no such file" error on macOS/Windows. Now checks runtime.GOOS first and prints "uname: not supported on darwin (Linux only)". Tests skip proc-dependent cases on non-Linux, with a dedicated TestUnameNonLinuxPlatform test verifying the error message. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Go tests (Linux-only via requireLinux): - Duplicate flags (-ss), all flags explicit (-snrvm), flag order independence (-mrvns), -a overrides individual flags - Partial proc tree (success and failure paths) - Whitespace trimming in proc values, empty proc file - Pipe integration, variable capture via command substitution - Context cancellation All-platform tests: - Help via -h and --help, stderr empty on help - Extra positional arguments ignored (POSIX behavior) YAML scenarios: - errors/unknown_flag — rejects unknown flags - basic/help — --help prints usage to stdout Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-25T20:08:00Z

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GNU uname rejects extra operands with exit 1: uname: extra operand 'foo' Our implementation was silently ignoring them. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-25T20:21:06Z

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Replace unbounded os.ReadFile with os.Open + io.LimitReader(4096). Prevents DoS if --proc-path points at a large file or FIFO instead of actual proc pseudo-files. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The test helper returned exit code 0 when runner.Run failed with a context cancellation error (no ExitStatus unwrapped). Now returns 1 for cancelled contexts, fixing TestUnameContextCancellation. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-25T20:34:05Z

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matt-dz · 2026-03-25T20:51:50Z

@codex conduct a comprehensive security and code review. ignore the symlink kernel file reads in uname reads.

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Check file type via fstat after open — reject FIFOs, sockets, etc. that could block indefinitely. Allow regular files and char devices (proc pseudo-files may appear as char devices on some configs). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-25T21:07:57Z

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os.Open on a FIFO blocks in open(2) before reaching the fstat type check, causing uname to hang when --proc-path points at a tree with mkfifo'd entries. Move the type check to os.Stat before os.Open so FIFOs are rejected without blocking. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-25T21:21:07Z

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The previous stat-then-open approach had a TOCTOU gap where an attacker could swap a regular file for a FIFO between the stat and open calls. Now opens with O_NONBLOCK (prevents blocking on FIFOs), then validates file type via fstat on the opened fd — atomic check. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-25T21:34:40Z

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Per AlexandreYang's review: move ReadKernelFile logic into a new builtins/internal/procsyskernel package for consistency with the existing procinfo, procnetsocket, and procnetroute internal packages. ProcProvider.ReadKernelFile now delegates to procsyskernel.ReadFile. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-26T13:16:11Z

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Add the same ".." traversal guard used by procnetroute and procnetsocket. Rejects paths like "/proc/../etc/passwd" before filepath.Clean can normalize them away. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

BoolP("s","s",...) registered --s as a long form. GNU uname --v prints the coreutils version (not kernel version), making --v incompatible. Use descriptive long names matching GNU coreutils: --kernel-name, --nodename, --kernel-release, --kernel-version, --machine, --all Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-26T14:12:24Z

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ReadFile's name parameter is currently hardcoded from uname.go, but the API is exported. Reject absolute paths, "..", and path separators in name to prevent path escape via the exported ReadKernelFile API. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add "Try 'uname --help' for more information." line to match GNU coreutils error format. Remove skip_assert_against_bash since uname is available on Ubuntu CI runners. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-26T14:30:14Z

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When /proc/sys/kernel/arch is unavailable (older kernels, restricted environments), fall back to runtime.GOARCH mapped to Linux kernel machine names (amd64→x86_64, arm64→aarch64, 386→i686, etc.). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-26T15:12:15Z

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runtime.GOARCH returns the compile-time target architecture, not the host system's architecture. With --proc-path pointing at a remote host's proc tree, the fallback would silently return wrong data. The proc file is the only correct source; if missing, fail honestly. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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Last 2.6 LTS (2.6.32) reached EOL February 2016. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Help now shows both short and long forms (e.g. -s, --kernel-name) matching the GNU coreutils style. Updated help scenario assertions to verify long option names are present. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

… scenarios - unknown_flag: pflag error format differs from GNU coreutils - help: GNU includes flags we don't support (-p, -i, -o, --version) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz · 2026-03-26T15:33:32Z

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chatgpt-codex-connector · 2026-03-26T15:44:28Z

Codex Review: Didn't find any major issues. 🎉

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AlexandreYang · 2026-03-26T15:54:03Z

@@ -0,0 +1,11 @@
+# skip: GNU uname --help includes flags we don't support (-p, -i, -o, --version)


Should we have scenario tests for each of the flags?

[Claude Opus 4.6] Cannot add scenario tests for flag output — the scenario test framework has no platform-skip mechanism, and uname reads from /proc (Linux-only). Scenarios fail on macOS and Windows CI runners. This is the same limitation documented in AGENTS.md for ip route:

"ip route show/ip route get happy-path scenario tests cannot be added. The scenario test framework has no platform-skip mechanism."

Flag coverage is in the Go tests (builtins/tests/uname/uname_test.go) which use requireLinux(t) to skip gracefully on non-Linux. Every flag (-s, -n, -r, -v, -m, -a) plus combined flags, flag ordering, and edge cases are covered there with a fake proc tree.

matt-dz and others added 4 commits March 25, 2026 15:44

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fix(uname): reject extra positional operands

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GNU uname rejects extra operands with exit 1: uname: extra operand 'foo' Our implementation was silently ignoring them. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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matt-dz and others added 2 commits March 25, 2026 16:30

fix(proc): bound ReadKernelFile reads to 4 KiB

1bd4097

Replace unbounded os.ReadFile with os.Open + io.LimitReader(4096). Prevents DoS if --proc-path points at a large file or FIFO instead of actual proc pseudo-files. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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matt-dz and others added 2 commits March 26, 2026 10:06

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matt-dz and others added 2 commits March 26, 2026 10:24

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matt-dz and others added 3 commits March 26, 2026 11:24

docs(uname): note /proc/sys/kernel/arch availability since Linux 2.6

3a96e33

Last 2.6 LTS (2.6.32) reached EOL February 2016. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs(test): add comments explaining skip_assert_against_bash in uname…

2407658

… scenarios - unknown_flag: pflag error format differs from GNU coreutils - help: GNU includes flags we don't support (-p, -i, -o, --version) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

matt-dz marked this pull request as ready for review March 26, 2026 15:48

matt-dz requested review from astuyve, julesmcrt and thieman as code owners March 26, 2026 15:48

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matt-dz added the verified/allowed_symbols label Mar 26, 2026

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Merged via the queue into main with commit c944642 Mar 26, 2026
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matt-dz deleted the matt-dz/implement-uname branch March 26, 2026 16:05

		@@ -0,0 +1,11 @@
		# skip: GNU uname --help includes flags we don't support (-p, -i, -o, --version)

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matt-dz commented Mar 25, 2026

Summary

Flags (POSIX)

Test plan

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