Recommended Free Tools
Linux administrators need different tools for different questions: what is running, what is slowing the system, which service owns a port, and what changed during startup. These nine tool groups cover common day-to-day checks, but they are not a universal ranking. Package names, command availability, and defaults vary by distribution; minimal installations may omit utilities that are common on full systems.
Use the command-line tools below for local inspection and focused troubleshooting. For a fleet, they complement rather than replace centralized metrics and alerting.
1. Inspect processes with ps and top
Start with the distinction between a snapshot and a live view. The Debian Reference Manual describes ps as a static view of process activity and top as an interactive, changing display; Red Hat makes the same distinction for RHEL 9. Use ps to capture what is running at a moment, and top to watch processes as CPU or memory use changes.
ps: useful for a one-time process listing or a command output you can inspect or save.top: useful when you need to observe changing resource use interactively.
Debian notes that the procps package provides basic process utilities including ps, top, kill, and watch. See the Debian Reference Manual, section 9.4, and Red Hat Enterprise Linux 9: Monitoring and managing system status and performance.
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2. Find resource pressure with vmstat, sar, and iostat
These utilities cover related but distinct views. vmstat reports current system activity across processes, memory, paging, block I/O, interrupts, and CPU. sar is for activity that has been collected over time, which helps answer whether a symptom is isolated or part of a recurring pattern. iostat focuses on loading across I/O devices.
- Use
vmstatwhen you need a broad view of current system state. - Use
sarwhen you need recorded activity rather than only a live snapshot; its usefulness depends on activity collection being configured and available. - Use
iostatwhen the question is specifically about device I/O load.
Red Hat documents these utilities in its RHEL 9 performance guide. Debian lists sar, iostat, and mpstat as part of sysstat in the Debian Reference Manual. Availability and collection defaults depend on the system.
3. Diagnose logs and boot time with journalctl and systemd-analyze
Logs and startup timing answer different questions. On systems using systemd, journalctl -b displays journal entries from the current boot, which is a practical starting point when a failure appeared after a restart. systemd-analyze provides timing and dependency views, including blame and critical-chain analysis, to help identify services associated with startup duration.
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Debian’s monitoring portal documents these commands and their uses in its monitoring guide. These systemd commands are relevant only where systemd and its journal are in use.
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4. Check sockets with ss and inspect traffic with tcpdump
ss prints socket statistics and helps inspect socket metadata, such as which network endpoints are present. Red Hat documents it as a socket tool that can be used instead of netstat. When the question is about what is actually passing over an interface, tcpdump captures packet-level communications. A socket listing and a packet capture are not interchangeable: one describes connections and socket state, while the other observes traffic.
Debian’s monitoring portal also lists iftop for observing network flows, a higher-level view than packet contents. Use packet capture deliberately, especially on shared or production networks. See the Red Hat RHEL 9 guide for ss and the Debian monitoring guide for tcpdump and iftop.
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5. See storage layout and usage with df, du, and lsblk
Storage troubleshooting usually needs two kinds of visibility: which filesystems or devices exist, and where space is being consumed. df and du are commonly used for filesystem capacity and directory usage, while lsblk presents block devices and their relationships. Check the manuals installed for your distribution before relying on exact options or output fields; those details are not uniform across all Linux systems.
These tools help distinguish a full filesystem from a device-layout issue, but they do not by themselves establish why a workload is slow. For device I/O activity, use iostat as described above.
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When a file cannot be changed or a port appears occupied, finding the process that holds the resource narrows the investigation. Debian’s Reference Manual describes lsof as a way to list files opened by a process and documents fuser for identifying processes using a file or socket. These are ownership checks; they do not replace inspecting the process or understanding why it has the resource open.
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Consult the Debian Reference Manual for these utilities. Installation and exact usage can vary by distribution.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.7. Trace a failing program with strace
When a process-level overview is not enough, strace traces system calls and signals. It can help investigate what a program asks the operating system to do when it fails, hangs, or behaves unexpectedly. Unlike routine overview tools such as ps and top, tracing is a focused diagnostic step: use it on the process and time window relevant to the problem.
The Debian Reference Manual describes strace in its monitoring and process-control section. Tracing can produce substantial output, so narrow the target and duration rather than treating it as a continuous monitoring method.
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8. Use your distribution’s package manager
Installing, updating, and removing software is a core administration task, but there is no single package-manager command that applies across Linux distributions. Use the package manager and official guidance for the distribution you administer; do not copy installation commands from a different distribution without checking their applicability. Debian’s system-administration portal treats package management as a core topic, but package-manager choice and command syntax are distribution-specific. See the Debian system-administration portal.
9. Synchronize files with rsync and plan for recovery
rsync synchronizes files and can be used as part of a backup workflow. Debian’s security tools page notes that it can preserve permissions, ownership, timestamps, and symbolic links. That makes it useful for copying files while retaining important metadata, but a synchronization utility alone is not a complete backup strategy. A reliable plan also needs independent copies and recovery checks so that a mistaken deletion or unusable copy does not defeat the purpose of the backup.
See Debian’s security tools and backup documentation for its description of rsync.
Quick Recap
How to choose the right tool for the question
| Question | Start with | Why |
|---|---|---|
| What processes are running right now? | ps |
It provides a process snapshot. |
| Which process is changing CPU or memory use? | top |
It provides an interactive, changing view. |
| Is system activity currently abnormal, or has it been recurring? | vmstat for current state; sar for collected activity |
They serve live aggregate and historical questions, respectively. |
| Is device I/O load the concern? | iostat |
It focuses on I/O-device loading. |
| What is in the current boot’s logs, or what delayed startup? | journalctl -b or systemd-analyze |
One reads current-boot journal entries; the other analyzes startup timing and dependencies on systemd systems. |
| Which sockets exist, or what packets are crossing an interface? | ss for sockets; tcpdump for packet capture |
They expose different layers of network activity. |
| Which process has a file or socket open? | lsof or fuser |
They help identify resource users. |
| What operating-system calls is a program making? | strace |
It provides focused system-call and signal tracing. |
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