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---
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tags:
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- shell
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- Linux
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id: t70u
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title: Processes
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tags: [operating-systems]
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created: Friday, June 21, 2024
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---
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# Processes (`ps`)
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# Processes
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`ps` allows us to control [user processes](The_kernel.md)
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from the shell.
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Programs are sequences of machine instructions stored in a file. However they do
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not work by themselves. Something needs to load the file's intructions into
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memory and direct the CPU to run the program. The OS does this via processes.
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The command in its most minimal application returns the following
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A process **is a running instance of a given program**. It can be thought of as
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a container in which a program runs. This container includes:
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```
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PID TTY TIME CMD
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2437 pts/2 00:00:01 zsh
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7112 pts/2 00:00:00 ps
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```
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- a copy of the program code loaded into memory
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- a memory address
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- other information about the state of the process
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With the `-e` modifier we can list more processes:
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```
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PID TTY TIME CMD
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1 ? 00:00:05 systemd
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2 ? 00:00:00 kthreadd
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3 ? 00:00:00 rcu_gp
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4 ? 00:00:00 rcu_par_gp
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5 ? 00:00:00 netns
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7 ? 00:00:00 kworker/0:0H-events_highpri
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9 ? 00:00:00 mm_percpu_wq
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11 ? 00:00:00 rcu_tasks_kthread
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12 ? 00:00:00 rcu_tasks_rude_kthread
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13 ? 00:00:00 rcu_tasks_trace_kthread
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14 ? 00:00:08 ksoftirqd/0
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15 ? 00:03:20 rcu_preempt
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16 ? 00:00:00 rcub/0
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17 ? 00:00:00 migration/0
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18 ? 00:00:00 idle_inject/0
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20 ? 00:00:00 cpuhp/0
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21 ? 00:00:00 cpuhp/1
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22 ? 00:00:00 idle_inject/1
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23 ? 00:00:00 migration/1
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```
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<dl>
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<dt>pid</dt>
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<dd>Process ID: every currently running process has a unique ID<dd>
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<dt>tty</dt>
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<dd>The terminal device where the process is running<dd>
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<dt>Time</dt>
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<dd>The amount of CPU time in minutes and seconds that the process has used so far. The total amount of time that the process has spent running instructions on the processor.<dd>
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<dt>cmd</dt>
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<dd>The command used to run the program. Note this can change during the running of the program.<dd>
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</dl>
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## Modifiers
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<dl>
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<dt><code>ps x</code></dt>
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<dd>Show all running processes<dd>
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<dt><code>ps ax</code></dt>
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<dd>Show all processes not just the ones you, the current user, own<dd>
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<dt><code>ps u</code></dt>
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<dd>Show detailed info on processes<dd>
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<dt><code>ps w</code></dt>
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<dd>Show full command names<dd>
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</dl>
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## Process termination
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The general schema is: `kill [pid]`. This allows for process clean-up. If this
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doesn't succeed you can force with `KILL [pid]` which will terminate the process
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immediately but is obviously more risky.
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We can also start/stop processes with modifiers on `kill`:
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- `kill -STOP pid`
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- `kill -CONT pid`
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## Related notes
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78
zk/ps.md
Normal file
78
zk/ps.md
Normal file
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@ -0,0 +1,78 @@
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---
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tags:
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- shell
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- Linux
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---
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# Processes (`ps`)
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`ps` allows us to control [user processes](The_kernel.md)
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from the shell.
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The command in its most minimal application returns the following
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```
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PID TTY TIME CMD
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2437 pts/2 00:00:01 zsh
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7112 pts/2 00:00:00 ps
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```
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With the `-e` modifier we can list more processes:
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```
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PID TTY TIME CMD
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1 ? 00:00:05 systemd
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2 ? 00:00:00 kthreadd
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3 ? 00:00:00 rcu_gp
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4 ? 00:00:00 rcu_par_gp
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5 ? 00:00:00 netns
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7 ? 00:00:00 kworker/0:0H-events_highpri
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9 ? 00:00:00 mm_percpu_wq
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11 ? 00:00:00 rcu_tasks_kthread
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12 ? 00:00:00 rcu_tasks_rude_kthread
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13 ? 00:00:00 rcu_tasks_trace_kthread
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14 ? 00:00:08 ksoftirqd/0
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15 ? 00:03:20 rcu_preempt
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16 ? 00:00:00 rcub/0
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17 ? 00:00:00 migration/0
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18 ? 00:00:00 idle_inject/0
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20 ? 00:00:00 cpuhp/0
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21 ? 00:00:00 cpuhp/1
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22 ? 00:00:00 idle_inject/1
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23 ? 00:00:00 migration/1
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```
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<dl>
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<dt>pid</dt>
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<dd>Process ID: every currently running process has a unique ID<dd>
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<dt>tty</dt>
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<dd>The terminal device where the process is running<dd>
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<dt>Time</dt>
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<dd>The amount of CPU time in minutes and seconds that the process has used so far. The total amount of time that the process has spent running instructions on the processor.<dd>
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<dt>cmd</dt>
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<dd>The command used to run the program. Note this can change during the running of the program.<dd>
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</dl>
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## Modifiers
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<dl>
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<dt><code>ps x</code></dt>
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<dd>Show all running processes<dd>
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<dt><code>ps ax</code></dt>
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<dd>Show all processes not just the ones you, the current user, own<dd>
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<dt><code>ps u</code></dt>
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<dd>Show detailed info on processes<dd>
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<dt><code>ps w</code></dt>
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<dd>Show full command names<dd>
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</dl>
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## Process termination
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The general schema is: `kill [pid]`. This allows for process clean-up. If this
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doesn't succeed you can force with `KILL [pid]` which will terminate the process
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immediately but is obviously more risky.
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We can also start/stop processes with modifiers on `kill`:
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- `kill -STOP pid`
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- `kill -CONT pid`
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|
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@ -10,13 +10,13 @@ tags:
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Once the [boot process](Boot_process.md) has completed and the bootloader has
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located the kernel and injected it into memory the first user space program
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runs: `init` (for _initialisation_). `init` is a [daemon](Daemons.md) process
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that continues running until shutdown and is responsible for starting all the
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processes that are prerequisites for user space. For example: network
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connections, disk access, user logins etc. `init` is the parent of all
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processes: PID1. Whilst it does a lot of its work in quick succession at boot
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time it is not limited to the this stage of the lifescycle but runs continuously
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in reponse to new user events.
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runs: `init` (for _initialisation_). `init` is a [daemon](Daemons.md)
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[process](./Processes.md) that continues running until shutdown and is
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responsible for starting all the processes that are prerequisites for user
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space. For example: network connections, disk access, user logins etc. `init` is
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the parent of all processes: PID1. Whilst it does a lot of its work in quick
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succession at boot time it is not limited to the this stage of the lifescycle
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but runs continuously in reponse to new user events.
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On Linux systems `systemd` is used to implement `init`.
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|
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