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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstalllsfd is a Linux command for inspecting open file descriptors, including files and sockets. The util-linux manual describes it as “intended to be a modern replacement for lsof(8) on Linux systems,” but says its command-line interface and output formats differ. Use it to inspect Linux processes and kernel-specific details; translate existing lsof commands rather than swapping the command name.
What is lsfd?
lsfd is a command in the util-linux collection that reports open file descriptors on Linux. Its view can include ordinary files, sockets, and other descriptor-associated objects. It is designed around Linux kernel information and supports Linux-specific features such as namespaces, so it is not a general Unix command.
The command was introduced in util-linux 2.38. Its formatting and filtering use Libsmartcols. The project’s wording is deliberate: lsfd is a modern lsof alternative for Linux, not a drop-in replacement. util-linux lsfd manual; util-linux 2.38 release notes.
How do you find which process has a file open?
Start with an expression that matches the reported name, or limit the scan to a process whose PID you already know:
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lsfd -Q 'NAME == "/path/to/file"'
lsfd -p 1234Replace the path and PID with the values you need. To inspect more than one known process, provide comma-separated PIDs:
lsfd -p 1234,5678The manual notes that -p is more efficient than collecting broadly and applying an equivalent PID expression with -Q. Expression filtering is useful when the criterion is something other than a known PID:
lsfd -Q 'PID == 1234'
lsfd -Q 'ASSOC == "exe"'The executable-association example is also shown in the util-linux 2.38 release notes. Consult the lsfd manual for expression syntax and available fields.
How do you list open descriptors and sockets?
List open descriptors
Run lsfd without filters to display open descriptors. The default table is useful for interactive inspection; for targeted output, select fields explicitly.
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View IP sockets
Use the address-family options to focus the view on IPv4 or IPv6 sockets:
lsfd -i4
lsfd -i6Inspect threads
Add -l to list at thread level when you need detail beyond the process-level view:
lsfd -lThese options and their behavior are documented in the lsfd manual.
How do you choose columns or produce JSON?
For a narrower table, pass a comma-separated column list to -o. For example:
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lsfd -o COMMAND,PID,TYPE,NAMETo discover column names accepted by your installed version, run lsfd -H or lsfd --list-columns. Column availability and behavior should be checked against that version’s manual.
For machine-readable output, use JSON:
lsfd -JRaw output can be requested with -r where appropriate. The manual also documents custom counters with --counter and summaries with --summary; combining a summary with JSON is supported only in the documented valid mode, so check the manual rather than assuming every option combination works.
Can you safely parse lsfd output in scripts?
Do not build a script around lsfd’s unqualified default table: the manual warns that default output may change. Pin the output you expect by selecting columns with -o, or use -J when a machine-readable format suits the task. Test the parser against the util-linux version deployed on the target system.
When the target PID is known, prefer -p PID over a broad scan followed by a PID condition in -Q; the manual specifically identifies the PID option as more efficient. For other predicates, use -Q and verify the expression and output fields in the installed manual.
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| Area | lsfd | lsof |
|---|---|---|
| Platform scope | Linux-specific; designed around Linux kernel data. | Used across a broader range of Unix-like systems. |
| Linux kernel details | Supports Linux-specific features such as namespaces. | Its platform coverage and interface are distinct from lsfd’s Linux-focused design. |
| Options and filters | Uses its own options, including -p, -Q, and socket-family selectors. |
Has a different command-line interface; expressions are not mechanically interchangeable. |
| Output | Offers column selection and JSON, while default output may change. | Has its own output conventions and parsers. |
| Portability | Appropriate for Linux systems with util-linux lsfd available. | Often better suited to workflows that must span Unix-like platforms. |
The comparison reflects the util-linux manual’s explicit warning that lsfd is not a drop-in lsof replacement. During migration, translate each command’s intent: check every option and filter, map the desired fields, and update any output parser. See the lsfd manual for lsfd’s interface.
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