This document discusses processes in Linux. It defines a process as a running instance of a program in memory that is allocated space for variables and instructions. All processes are descended from the systemd process. It describes process states like running, sleeping, stopped, and zombie. It also discusses process monitoring and management tools like top, ps, kill, and setting process priorities with nice and renice. Examples are provided on using ps to view specific processes by user, name, ID, parent ID, and customize the output.

1. Process Management in Linux
Manikandan.C
9677718889
Senior Redhat Trainer

2. !!!Process!!! what it is ??
• A program is a series of instructions that tell the
computer what to do.
• When we run a program, those instructions are
copied into memory and space is allocated for
variables and other stuff required to manage its
execution.
• This running instance of a program is called a
process and it's processes which we manage.

3. For Example
create a file called user under /bin.
# vim /bin/user
useradd king
:wq
# chmod a+x /bin/user
Giving a command user an user named king will be created as a
result.
# user

4.  1st -> As soon as we open a terminal a process name bash
is started. . Rite ???? Tis systemd the parent process for
all descendant process is responsible.
 2nd -> users are creating process by command to execute
some program that is process.
Who is that
creating process
??

5. Description of process
• Like humans even process has the information like
when it is created,
• address space of allocated memory,
• security properties including ownership credentials
and privileges,
• one or more execution threads of program code, and
the process state.
NOTE: All processes are descendants of the first system process SYSTEMD.

6. Small briefing on -> fork, pthreads.
FORK:
Fork is nothing but an existing parent process
duplicates its own address space and create a
new child process structure.
Pthreads:(POSIX THREADS)
Parallel execution model which allows a
program to control multiple different flows of
work that overlap in time.
Mainly for the multitasking purpose

7. Linux Process states
A process (which includes a
thread) on a Linux machine can
be in any of the following states –
RUNNING
SLEEPING
STOPPED
ZOMBIE

8. Types of terminal
• Tty and pty:
 tty is called teletype where user interacts
with the system.
 Pty is called as the psuedoterminal where the
process uses as its terminal in the background.
And many would have came across the pts
terminal where pts is nothing but the slave
part of pty terminal.

9. RUNNING
• When a command triggers a program, the process
is automatically
Name Flag Kernel-defined state and description
Running R TASK_RUNNING - The process is either
executing on a CPU or waiting to be
executed.

10. Sleeping
Sleeping
S
TASK_INTERRUPTIBE: The
process is waiting for some
condition: a h/w request ,
system resource access or
signal. When an event or
signal satisfies the condition,
the process returns to
Running.
D TASK_UNINTERRUPTIBLE -
Like TASK_INTERRUPTIBLE,
except that delivering a
signal to the sleeping process
leaves its state unchanged.
K TASK_KILLABLE: identical to D
state, but modifies to allow
the waiting task to respond
to a signal to be killed.

11. STOPPED
Name Flag Description
Stopped
T TASK_STOPPED: The process has been
stopped, usually by being signaled by
a user or another process . The
process can be continued (resumed)
by another signal to return to
Running.
T TASK_TRACED: A process that is being
debugged is also temporarily Stopped
and shares the same T flag.

12. ZOMBIE
Name Flag Description
Zombie
Z EXIT_ZOMBIE - Process execution is
terminated, but the parent process
has not yet issued a wait4( ) or
waitpid( ) system call. The OS will
not clear zombie processes until
the parent issues a wait()-like call
X EXIT_DEAD: when the parent
cleans up (reaps) the remaining
child process structure, the process
is now released completely. This
state will never be observed in
process-listing utilities.

13. Process
Process
monitoring(top,sar,watch)
Managing process (ps)
Killing process(kill, pkill)
Setting priority(nice,renice)

14. Process commands usage
top
• Monitoring cpu
memory and
process
utilization
• Kill user and
system process
Kill
Priorities:
Nice
,renice >

15. Examples
> To display all the process:
# ps –ef
# ps ax
> To display process by user:
# ps –f -u apache,postfix
# ps –f -u linuxguy

16. > To show process by name or process Id:
#Ps -C apache2
# ps -f -p 2764
> To get the information on particular process:
# ps –ef | grep postfix

17. > To display threads of process:
# ps -p 2764 –L
> To know the parent id of the process:
# ps –ppid 2543
> To customize the view of process display:
Ps –eo pid,uname,pcpu,pmem,comm
> To list process in hierarchy:
# ps –ef - - forest

18. Thanks for watching