Run a command and see real, user and sys time to find where CPU and wall time are spent. 14.05.2026 | reading time: 3 min Want to know how long a command really takes and how much CPU it uses? The Linux "time" command runs a program and then reports wall-clock time along with CPU time spent in user and kernel mode, making it a first step for spotting performance issues. Live example Try this simple test to see the report: ```bash $ time sleep 1 real 0m1.002s user 0m0.000s sys 0m0.001s ``` The output appears after the command finishes and shows real, user and sys lines for easy reading. What those numbers mean The real value is wall-clock time from start to finish; user is CPU time spent in user-mode code; sys is CPU time spent in kernel-mode on behalf of the process; together they show whether the job is CPU-bound or waiting on I/O or other resources. Advanced usage Use the POSIX-friendly option `-p` for portable output or call the external GNU version `/usr/bin/time -v` for verbose resource details such as maximum resident set size and I/O counts; GNU time also accepts `-f` or `--format` with format specifiers like "%M" to print peak memory usage. Practical tips Remember that many shells include a builtin time while `/usr/bin/time` is the external tool; the timing report is written to stderr by default so redirect with `2>` or capture with `2>&1`; to force the external tool use `command time` and to measure entire pipelines place time before the pipeline. Related tools for deeper analysis When you need more than elapsed and CPU time, move on to tools that trace system calls, inspect CPU events or show live process usage; these tools expose different angles of performance beyond what time reports. Next steps Start with simple timings, then combine time with redirections and the GNU format options to collect reproducible measurements; profile with more powerful tools when needed and consider formalizing skills with CompTIA Linux+ or LPIC-1 exam preparation at bitsandbytes.academy for intensive practice. Join Bits & Bytes Academy First class LINUX exam preparation. utilities processes scripting troubleshooting
