> For the complete documentation index, see [llms.txt](https://dev117uday.gitbook.io/notes-md/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dev117uday.gitbook.io/notes-md/linux/linux-commands-part-9-10.md).

# Linux Commands Part 9 - 10

Tags: linux-com-book

* User accounts are defined in the `/etc/passwd` file
* groups are defined in the `/etc/group` file

![file types](/files/kucT186DiPoDjMuijCcq)

![permission attributes](/files/fOkCYssSWSTZ3IeqEhTS)

![chmod permission symbolic notation](/files/0g9O73WmCWhPOQycy3TR)

![chmod notation example](/files/AR4tzpGnXfLa3wRQl2fk)

![file permission in octal](/files/ZHUxizpCuXYvw2XDFPOS)

### chown and chgrp

* `chown` : to change the file ownership 
* `chgrp` : to change the group

`d|rwx|rwx|rwx`

* d : directory
* 1st block for user
* 2nd block for group (of user)
* 3rd block for other

```
chmod u=rwx test.sh
chmod g=rwx test.sh
chmod o=rwx test.sh
chmod go-wx test.sh
chmod 744 test.sh
```

numbering system : read = 4 write = 2 exec = 1

## Processes

* When a system starts up, the kernel initiates a few of its own activities as processes and launches a program called init
* init, in turn, runs a series of shell scripts (located in /etc) called init scripts
* The fact that a program can launch other programs is expressed in the process scheme as a parent process producing a child process

```bash
# to look at process 
ps 

# to show all process regardless of terminal
ps x

# output 
PID TTY      STAT   TIME COMMAND
   1876 ?        Ss     0:02 /usr/lib/systemd/systemd --user
   1881 ?        S      0:00 (sd-pam)
   1895 ?        Ss     0:12 /usr/bin/appimagelauncherd
   1902 ?        Sl     0:00 /usr/bin/gnome-keyring-daemon --daemon
   1915 tty2     Ssl+   0:00 /usr/libexec/gdm-wayland-session /usr/
   1917 ?        Ss     0:00 /usr/bin/dbus-broker-launch --scope us
   1920 ?        S      0:02 dbus-broker --log 4 --controller 9 --m
   1923 tty2     Sl+    0:00 /usr/libexec/gnome-session-binary
   1982 ?        Ssl    0:00 /usr/libexec/gnome-session-ctl --monit
   1983 ?        Ssl    0:00 /usr/libexec/uresourced --user
   1986 ?        Ssl    0:00 /usr/libexec/gnome-session-binary --sy
   1990 ?        Ssl    0:00 /usr/libexec/gvfsd

# for a detailed look
ps aux

# output
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.0  0.2 173328 17748 ?        Ss   16:29   0:01 /usr/lib/systemd/systemd
root           2  0.0  0.0      0     0 ?        S    16:29   0:00 [kthreadd]
root           3  0.0  0.0      0     0 ?        I<   16:29   0:00 [rcu_gp]
root           4  0.0  0.0      0     0 ?        I<   16:29   0:00 [rcu_par_gp]
root           5  0.0  0.0      0     0 ?        I<   16:29   0:00 [netns]
root           7  0.0  0.0      0     0 ?        I<   16:29   0:00 [kworker/0:0H-events_highpri]
root           9  0.0  0.0      0     0 ?        I<   16:29   0:00 [kworker/0:1H-events_highpri]
root          10  0.0  0.0      0     0 ?        I<   16:29   0:00 [mm_percpu_wq]
root          11  0.0  0.0      0     0 ?        I    16:29   0:06 [kworker/u32:1-blkcg_punt_bio]
root          12  0.0  0.0      0     0 ?        I    16:29   0:00 [rcu_tasks_kthread]
root          13  0.0  0.0      0     0 ?        I    16:29   0:00 [rcu_tasks_rude_kthread]
root          14  0.0  0.0      0     0 ?        I    16:29   0:00 [rcu_tasks_trace_kthread]
root          15  0.0  0.0      0     0 ?        S    16:29   0:00 [ksoftirqd/0]
```

![process state diagram](/files/hU7KS2NhOQvJGkAwOVym)

**Information shown by top**

![top field information](/files/lbdJGJp9AAzSNvAV1aDK)

![top field information](/files/A2VACHzeRFUFQNVq9dZC)

* to kill a process : `kill -signal [PID]`

![process signals](/files/R84cIKURNkznY1GSDj72)

![process signals part 2](/files/vtkO0HEQFv6mEJHbOl2Y)

![process signals part 3](/files/5LQ1M10GPgJp8iuLEZA1)