Signal

A signal is a software input delivered to a process

id code description
1 SIGHUP Hangup - report term of the process of terminal.
2 SIGINT keyboard interrupt ctrl + C
3 SIGQUIT quit ctrl + \
9 KILL kill unblockable
15 SIGTERM terminate (allows self cleanup)
18 SIGCONT continue
19 SIGSTOP stop, unblockable
20 TSTP keyboard stop

  • pkill is used to send a signal to one or more processes which match selection criteria. (command name, a process owned by a user, all system-wide processes)

  • pgrep like pkill list processes but does not kill them.

  • w lists user’s login sessions

  • in TTY section pts/N represent graphical term or remote login session while ttyN represents system console / alternate console / term device

  • uptime is used to display the current load average. It prints the current time, how long the machine has been up, how many user sessions are running, and the current load average. 1,5,15 mins

  • The top program is a dynamic view of the system’s processes

PERFORMANCE TUNING

Tuned provide profiles: Power-saving and Performance boosting Tuned profiles:

  • balanced (compromise between power saving and performance)
  • desktop (faster response of interactive apps)
  • througput-performance (max throughput)
  • latency-performance (ideal for servers that require low latency but consumes power)
  • network-latency (from latency-perf, but requires add network tuning)
  • network-throughput (from throughput, add. network tuning for max network throughput)
  • powersave (max powersaving)
  • oracle (optimized for oracle database loads based on throughput-performance)
  • virtual-guest (tunes for max perf. if it runs on vm)
  • virtual-host (tunes for max perf. if it acts as a host for vms)
  • tuned-adm is used to change tuned daemon settings tuned-adm list , tuned-adm profile , tuned-adm active , tuned-adm recommend

INFLUENCING PROCESS SCHEDULING

default scheduling policy: SCHED_OTHER (SCHED_NORMAL), processes can still be given a relative priority. (nice value -20<=x<20) usually 0

  • Higher nice value means lower priority, (easily gives up CPU usage - nice guy)
  • only a root user can reduce the nice level of a process. Unprivileged users can increase nice level of their own processes.

Displaying nice level

ps -o pid,comm,nice,pcpu