Processes, Services, & Daemons

All process by all users :

ps aux | less

VSZ : Virtual Memory Size in KB
RSS : Resident Set Size ( physical Memory , not swapped )
TTY : Started in Background NOT in Terminal if it as '?'
STAT : State of the running process
TTY : Terminal

This above command will remove or filter with -v or It won't appear in the screen.

Below is the Tree , how the process started one by one,

pstree | less

ps aux | sort -nk 4 | tail -3

( Here sort by fourth column i.e., Memory and tail 3 is the last three value which is consuming more memory )

Only giving 'ps' will show the process which are running in this terminal alone,

aux --> will provide all process in all terminal.

Monitoring :

1. ps
2. ps aux | grep syslogs
3. top

PR : Priority

Once you press 'd' then it will prompt for entering the number. Now we can change from 3 secs delay to 1 secs delay also like below ,

Press 'f' , it will show the abbreviation of the given name which shows n 'top' command.

F for select
Space-Bar for deselect the column
Q to go-back
S for which column you need to sort

Top command to batch file ,

top -n 5 -b > /tmp/top_output.txt ( 5 is the Iteration & out to a file )

Killing a process :

& - will send it to run at the back-end.

15 - Graceful shutdown
9 - Forceful

NO SIGNAL - it saves and gets terminated
-9 - its killed

We should send only PID ? we can also send process name.

pgrep --> greps the process id

kill -1 cmd & --> even if you close the terminal , this killing process will run at the back-end.

PROCESS PRIORITY :

1. Focus on 6th column , nice value.
2. This is the priority value given to any process accordingly.
3. You can reassign the priority or assign while start of the process itself.

Where these PID is stored ?

1. /proc/

Process Information :

cat /proc/cpuinfo

File System :

df -h ( h human readable )
watch -n 5 df -h ( for every 5 secs watch the df -h )

Logs :

1. tail is see the last lines in a file or log.
2. '-f' is used to check the real time logs.
3. /var/log --> system logs

If you want to check process which are running by specific user in TOP ,

top -u

In the below you can see , no terminal information.

But here you can see terminal information , but editing the TOP command like F , SPACE-BAR , S & Q

If you want to check only one PID ,

STARTING & STOPPING OF SERVICES :

1. In TOP command , you can see TTY as '?' , that means these process are started by Operating SYSTEM not manually.
2. systemctl and service commands are used , which is discussed in detail in other blog.
3. systemctl list-unit-files --type service | less
4. Static means ONLY ONE TIME WHEN NEEDED.

What is SYSTEMD ?

All system dot files will be here , which is used to run the daemon.

System files are present here also,

*systemctl list-unit-files --type service --all | less
*

This is the list of services which are managed by " SYSTEMD ".

There are 3 section if you notice , UNIT - it will say the dependencies , SERVICE - service level information & WANTED - Environmental files .

The environmental file contains the , details of the environmental details of the specific service.

These are the service which are managed by SYSTEMD,

SYSTEMD can manage all CHILD process also ,

systemctl list-unit-files | less
proc-sys-fs-binfmt_misc.automount
dev-hugepages.mount

These type of extension is also maintained by SYSTEMD.

Lets displace the dependencies of services ,

All the immediate dependencies are listed.

RUNLEVEL :

Now its called TARGETS. (TBD)

Also SYSTEMD can used in LOGGING, these are called JOURNALS.

Some text will be RED colour , that means it as some issue.

Latest logs,

Real time logs ,

Logs of Current BOOT session,

Note :

1. syslog - which is logged when the server starts , all starting logs will be stored here.

ps aux | grep syslog

1. Zombie task - Which didn't shutdown properly.
2. SIGNAL 15 is the default killing process. ( graceful shutdown )
3. Here in Linux , services are called daemon.
4. If you are creating a service to be started at the time BOOTING , then a symbolic link will be created.
5. Script10 service ( this can be used to replace the CRON Jobs ) which is by SYSTEMD
6. Mask - it will make a symbolic link to null and never can be started.