computer science

Sar (Unix)

Sar (Unix) is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sar (Unix) rather than just read about it. In short: System Activity Report (sar) is a Unix System V-derived system monitor command used to report on various system loads, including CPU activity, memory/paging, interrupts, device load, network and swap space utilization. Sar uses /proc filesystem for gathering information.

Key takeaways

Sar (Unix) belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sar (Unix) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sar (Unix) from memory before moving on to harder problems.

Reference excerpt

System Activity Report (sar) is a Unix System V-derived system monitor command used to report on various system loads, including CPU activity, memory/paging, interrupts, device load, network and swap space utilization. Sar uses /proc filesystem for gathering information.

Platform support Sar was originally developed for the Unix System V operating system; it is available in AIX, HP-UX, Solaris and other System V based operating systems but it is not available for macOS or FreeBSD. Prior to 2013 there was a bsdsar tool, but it is now deprecated. Most Linux distributions provide sar utility through the sysstat package.

Syntax sar [-flags] [ -e time ] [ -f filename ] [-i sec ] [ -s time ]

-f filename Uses filename as the data source for sar. The default is the current daily data file /var/adm/sa/sadd. -e time Selects data up to time. The default is 18:00. -i sec Selects data at intervals as close as possible to sec seconds.

Example

Sysstat package Additional to sar command, Linux sysstat package in Debian, RedHat Enterprise Linux and SuSE provides additional reporting tools:

sar(1): Collect, report, or save system activity information. – Linux User Commands Manual sa1(8): Collect and store binary data in the system activity daily data file. – Linux Administration and Privileged Commands Manual sa2(8): shell variant of sar, supporting the same flags as sar command which write a daily report in the /var/log/sa directory. – Linux Administration and Privileged Commands Manual sadf(1): , similar to sar but can write its data in different formats (CSV, XML, etc.). This is useful to load performance data into a database, or import them in a spreadsheet to make graphs. iostat(1): reports basic CPU statistics and input/output statistics for devices, partitions and network filesystems. – Linux User Commands Manual mpstat(1): reports individual or combined processor related statistics. – Linux User Commands Manual pidstat(1): reports statistics for Linux tasks (processes) : I/O, CPU, memory, etc. – Linux User Commands Manual nfsiostat(1): reports input/output statistics for network filesystems (NFS). – Linux User Commands Manual cifsiostat(1): reports I/O statistics for CIFS resources. – Linux User Commands Manual

See also atopsar Nmon sag - "system activity graph" command ksar- BSD licensed Java-based application to create graph of all parameters from the data collected by Unix sar utilities. CURT, IBM AIX CPU Usage Reporting Tool isag, tcl based command to plot sar/sysstat data

References sar(1) – Solaris 11.4 User Commands Reference Manual Easy system monitoring with SAR (IBM developerWorks) System Activity Reporter (Softpanorama) Article on sar at Computerhope

Footnotes

Illustrations

Worked examples

Example 1 — a first encounter with Sar (Unix)

Start with the simplest possible case. Write down what Sar (Unix) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sar (Unix) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sar (Unix) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sar (Unix)

In research: Sar (Unix) appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sar (Unix) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sar (Unix) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer performance, Job scheduling, System administration, so understanding it makes those chapters shorter.
In everyday life: Look for Sar (Unix) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sar (Unix) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sar (Unix) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sar (Unix) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sar (Unix) in simple terms?

Why does Sar (Unix) matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sar (Unix)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sar (Unix).