Components of a Process:
1. Process Identifier – PID
2. Parent Process ID – PPID
3. UID and EUID – User Identification Number UID and End User ID
4. GID and EGID – Group Identification number and End User Group Identification number
Life Cycle of a Process
To create a new process a process copies itself with a fork system call. Fork creates a copy of the original. the fork process has a distinct PID the parent is the Original PID – also that is the PPID.
Process Signal
There are 4 kinds signals.
1. inter process communication signals
2. as terminal driver signals to kill, interrupt, or suspend processes when special keys such as
a. <Control C>
b. <Control Z>
3. Signals that can be sent by the administrator (with KILL) to achieve various results.
4. Kernel can send when a process commits an infraction such as division by Zero (0).
we need to know about the below signals:
From Unix System Administration Hand Book – 3rd Edition – By Evi Nemeth et all | ||||||
sl.no | Name | Description | Default | Can Catch? | Can Block? | Dump Core? |
1 | HUP | hangup | Terminate | Yes | Yes | No |
2 | INT | Interrupt | Terminate | Yes | Yes | No |
3 | QUIT | quit | terminate | Yes | Yes | Yes |
9 | KILL | kill | Terminate | No | No | No |
BUS | Bus Error | Terminate | Yes | Yes | Yes | |
SEGV | Segmeant Fault | Terminate | Yes | Yes | Yes | |
15 | TERM | Terminate | Terminate | Yes | Yes | No |
STOP | stop | stop | No | No | No | |
TSTP | keyboard stop | stop | Yes | Yes | No | |
CONT | Continue After stop | Ignore | Yes | No | No | |
WINCH | window changed | Ignore | Yes | Yes | No | |
USR1 | Used-defined | Terminate | Yes | Yes | No | |
USR2 | User Defined | Terminate | Yes | Yes | No |
Process States
- Runnable
- Sleeping
- Zombie
- Stopped
Resource Requiring Process Waits
- No Wait
- Willing to Wait
Nice and Renice – Influence Scheduling Priority. We need this to reduce “Log Sync Waits”
To monitor the processes ‘ps’ . Another monitoring processes command is top.
Runaway Processes
There are 2 types of Runaway Processes. A resource hog is one type of user process that is runaway resource hog. another one is a system process that suddenly go berserk and exhibit wild behavior.