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CompTIA Linux+ > 3.4 Init Scripts > Flashcards

3.4 Init Scripts Flashcards

2
Q

What is the role and function of init scripts?

A

Init scripts determine which services and daemons are configured at various runlevels.

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3
Q

Which distribution stores the init scripts in the /etc/rc.d/init.d directory?

A

System V distributions store the init scripts in the /etc/rc.d/init.d directory.

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4
Q

What does the /etc/init.d/rc5.d directory contain?

A

The /etc/init.d/rc5.d directory contains init scripts for services configured for runlevel 5.

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5
Q

How would you view what init scripts are available in your distribution?

A

You can view the init scripts available by examining the /etc/rc.d/init.d directory (System V distributions) or the /etc/init.d directory (BSD distributions).

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6
Q

What command runs an init script?

A

The service command runs an init script.

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7
Q

What identifier kills or starts an init script?

A

The ‘K’ identifier kills an init script, while the ‘S’ identifier starts an init script.

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8
Q

What is involved in init script configuration?

A

Specifying whether specific daemons start at a specified runlevel.

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9
Q

Where are init scripts stored?

A

Init scripts are stored in /etc/init.d (BSD distribution) or /etc/rc.d/init.d (System V distribution).

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10
Q

What are some features of init scripts?

A
  • They are configured differently for BSD and System V distributions.
  • They have symbolic links that are stored in subdirectories that correspond to the runlevel under which each script should start.
  • They can be started and stopped manually.
  • They are started at boot using the init script.
  • They contain code that determines the appropriate runlevels on which the script can operate.
  • Configuration commands use code in the scripts to configure the appropriate levels at which scripts can start and stop.
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11
Q

What is the code inside an init script that determines appropriate runleves on which the script can operate?

A
  • The default-start line defines the runlevels in which the script starts by default.
  • The required-start line defines services that must be running before this service can start.
  • The should-start line defines the services that are recommended to start before this service starts.
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12
Q

What does the rc script do?

A

The rc script (BSD and System V) switches between runlevels.

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13
Q

What does the halt script do?

A

The halt script (BSD and System V) stops and reboots the computer. It runs when the init 0 or init 6 commands are invoked.

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14
Q

What does the boot script do?

A

The boot script (BSD) is run by the init process when a computer starts. It runs the scripts contained in /etc/init.d/boot.d and performs tasks that include:

  • Loading the kernel module
  • Checking the file system
  • Setting the system clock
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15
Q

What does the rc.sysinit script do?

A

The rc.sysinit script (System V) is run by the init process when a computer starts. This script performs tasks that include:

  • Loading the kernel module
  • Checking the file system
  • Setting the system clock
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16
Q

What does the boot.local script do?

A

The boot.local script (BSD) runs specific tasks at startup as specified by the administrator. It is where you put commands you want to run every tim ethe system starts.

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17
Q

What does the rc.local script do?

A

The rc.local script (System V) runs specific tasks at startup as specified by the administrator. It is where you put commands you want to run every tim ethe system starts.

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18
Q

How does init determine the default runlevel at boot time?

A

At boot time, init uses the /etc/inittab file to determine the default runlevel, such as runlevel 5.

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19
Q

Given a specified runlevel, how does init know which processes to start?

A

The init process looks at the directory associated with the runlevel to determine what processes to start. The directory for runlevel 5 is named rc5.d. Additional directories named rc0.d through rc6.d specify what processes to start for each runlevel.

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20
Q

What kinds of files do the rc directories contain?

A

Each rc directory contains symbolic links that point to a specific init script in /etc/init.d or /etc/rc.d/init.d. Init follows the links and runs the scripts to start or stop processes. Init repeats the process using the appropriate rc directory whenever the runlevel changes.

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21
Q

What do the names of the symbolic links in the rc directories mean?

A
  • Link names starting with an S start a script for the runlevel.
  • Link names starting with a K kill a running process when the computer changes runlevels.
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22
Q

What does the service command do?

A

Manages the current state of a daemon.

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23
Q

What are the options of the service daemon_name command?

A
  • start starts a daemon that is not currently running.
  • stop halts a running daemon.
  • restart stops and restarts a daemon.
  • reload requests that a daemon read and apply its configuration files without stopping.
  • status shows the status of a single daemon or daemons.
  • –status-all shows the status of all daemons.
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24
Q

Aside from the service command, how else can you control a daemon init script?

A

You can use the absolute path to the daemon script and the option to configure the daemon (e.g., /etc/rc.d/init.d/httpd stop).

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25
Q

What does the insserv command do?

A

It configures default runlevels for a daemon on a BSD distribution.

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26
How does the **insserv** command determine the default runlevels for a daemon and dependent daemons?
It references the INIT INFO script section of each daemon to determine the default runlevels for the daemon and dependent daemons.
27
What does the command **insserv *script\_name*** do?
Starts the script and associated daemon at the runlevels specified in the *init block* of the script code.
28
What does the command **insserv -r *script\_name*** do?
Keeps the script and associated daemon from starting at any runlevel.
29
What does the command **insserv -d *script\_name*** do?
Restores the script and associated daemon to default runlevels defined in the *init block* of the script code.
30
What does the **chkconfig** command do?
Configures default runlevels for a daemon on a *System V distribution*.
31
What does the comand **chkconfig --add*script\_name*** do?
Adds a new service to be managed by **chkconfig**, and makes sure the service has a start or kill entry at every runlevel. E.g., **chkconfig --add atd**.
32
What does the comand **chkconfig --del*script\_name*** do?
Removes a service from **chkconfig** management, and removes symbolic links to the service from **/etc/rc0-6.d**. E.g., **chkconfig --del ldap**.
33
What does the comand **chkconfig --level *runlevel(s) script\_name*** do?
Specifies the runlevel(s) to which a service should belong. E.g., **chkconfig --level 5 lpd**
34
What does the comand **chkconfig --level *runlevel(s) script\_name* on** do?
Enables the service in the specified runlevels. If **--level *runlevels*** is omitted, defaults to runlevels 2 thorugh 5. E.g., **chkconfig ypxfrd on**.
35
What does the comand **chkconfig --level *runlevel(s) script\_name* off** do?
Disables the service in the specified runlevels. If **--level *runlevels*** is omitted, defaults to runlevels 2 thorugh 5. E.g., **chkconfig --level 345 nfslock off**.
36
What does the comand **chkconfig *script\_name* reset** do?
Resets the service to the default runlevels specified in the init script.
37
What does the comand **chkconfig --list** do?
Lists all services and their runlevels.
38
What does the command **chkconfig -l** do?
In BSD distributions, lists services and their runlevels.
39
What does the command **chkconfig -s** do?
In BSD distributions, specifies the level to which a service should belong.
40
What is *upstart*?
*Upstart* is an event-based replacement for the **/sbin/init** daemon; it will start and stop tasks and services whenever the Linux system enters a specific runlevel, but will also start and stop services upon receiving information that something on the system has changed (known as an event).
41
What are the *upstart* runlevels?
* **0** - halt state * **1** - single user mode * **2** - graphical, multi-user mode with networking (Default) * **3**, **4**, **5** - same as runlevel 2, but not used * **6** - reboot (the system restarts itself)
42
What is a *job* in the context of *upstart*?
A *job* is a series of instructions that **init** reads which typically include a *program* and the name of an *event*. The Upstart **init** daemon runs the *program* when the *event* is triggered. *Jobs* are divided into *tasks* and *services*.
43
What is a *task* in the context of *upstart*?
A *task* is a *job* that performs its work and returns to a waiting state when it is done.
44
What is a *service* in the context of *upstart*?
A *service* is a *job* that does not normally terminate by itself. The **init** daemon monitors each service, restarting the service if it fails and killing the service when it is stopped manually or by an event.
45
What does the **start** command do in the context of *upstart*?
Starts a daemon that is not currently running. (This is a symbolic link to the **initctl** command.)
46
What does the **stop** command do in the context of *upstart*?
Halts a running daemon. (This is a symbolic link to the **initctl** command.)
47
What does the **restart** command do in the context of *upstart*?
Stops and restarts a daemon. (This is a symbolic link to the **initctl** command.)
48
What does the **reload** command do in the context of *upstart*?
Requests that a daemon read and apply its configuration files without stopping. (This is a symbolic link to the **initctl** command.)
49
What does the **runlevel** command do in the context of *upstart*?
Displays the runlevel information. (This is a symbolic link to the **initctl** command.)
50
Does *upstart* support the **/etc/inittab** file?
Yes, but it is deprecated.
51
Which commands are used to change the current runlevel on systems that use *upstart*?
The **reboot**, **shutdown**, and **telinit** commands are used to change the current runlevel on systems that use *upstart*.
52
What specifies the default runlevel on systems that use *upstart*?
The `DEFAULT_RUNLEVEL` environment variable in the **/etc/init/rc-sysinit.conf** configuration file sets the default runlevel on systems that use *upstart*.
53
What is *systemd*?
*Systemd* is a replacement for both the **/sbin/init** daemon and *upstart*, and is designed to allow services to be started in parallel at system startup.
54
What are important characteristics and features of *systemd*?
* It is compatible with SysV and Linux Standards Base (LSB) init scripts * It uses socket and D-Bus activation for starting services * It allows you to start daemons on-demand * It tracks processes using Linux control groups * It supports snapshotting and restoring of the system state
55
What are *control groups* in the context of *systemd*?
*Control groups* (AKA *cgroups*) are used to track processes (instead of process IDs) for *systemd*.
56
What are important characteristics of *control groups* (*cgroups*)?
* A *cgroup* is a collection of processes that are bound together by common criteria. * *Cgroups* are hierarchical. They are organized into parent-child relationships; a child group inherits parameters from its parent group.
57
What comand is used to manage services and runlevels on systems that use *systemd*?
The **systemctl** command manages services and runlevels on systems that use *systemd*.
58
What does the **systemctl** command do?
On systems that use *systemd*, the **systemctl** command manages services and runlevels. It combines the functionality of both **service** and **chkconfig**.
59
What specifies the default runlevel on systems that use *systemd*?
The **/etc/systemd/system/default.target** symbolic link controls the default runlevel on systems that use *systemd*. It links to one of the files in the **/lib/systemd/system/** directory. Examples: * **default.target** - default file * **multi-user.target** - runlevel 3 * **graphical.target** - runlevel 5
60
Initialization (init) sequence on BSD distributions.
1. Execute /etc/init.d/boot, which executes scripts in /etc/init.d/boot.d 2. Process /etc/inittab to determine the appropriate runlevel 3. Run the initialization scripts that correspond to the appropriate runlevel 4. Execute /etc/init.d/boot.local
61
Initialization (init) sequence on System V distributions.
1. Execute /etc/rc.d/rc.sysinit 2. Process /etc/inittab to determine the appropriate runlevel 3. Run the initialization scripts that correspond to the appropriate runlevel 4. Execute /etc/init.d/boot.local
62
Key characteristics of *upstart*.
* Developed for Ubuntu * Asynchronous * Event-based * * Receives notification of events from other processes * Runs jobs (tasks or services) when certain events occur * Responds to runlevel changes just like init * Dynamically manages services based on events * Can determine if service has stopped and can restart automatically
63
Key characteristics of *systemd*.
* Drop-in replacement for **init** * Compatible with init scripts. * Can start services in parallel, rather than in serial * Dramatically reduces time to get system up-and-running * Uses sockets and D-Bus activation * Tracks processes with control groups * Supports snapshots
64
Which command is used to manage services and runlevels in *systemd*?
The **systemctl** command manages services and runlevels on systems that use *systemd*. It combines the functionality of **service** and **chkconfig**.
65
How do you switch to runlevel 5 on systems that use *systemd*?
**systemctl isolate runlevel5.target** or **systemctl isolate graphical.target**
66
What is the file that controls default runlevel on systems that use *systemd*?
**/etc/systemd/system/default.target**, which is a symbolic link to a runlevelX.target regular file.
67
What is the command to view runlevel targets on systems that use *systemd*?
**systemctl list-units --type=target**
68
What is the syntax of the command to change or view the state of services on systems that use *systemd*?
**systemctl start|stop|restart|status *service\_name*.service**
69
What is the syntax of the command enable or disable services on systems that use *systemd*?
**systemctl enable|disable|is-enabled *service\_name*.service**
70
Where are the *systemd* runlevel targets stored?
**/lib/systemd/system**
71
How is the default runlevel set in *systemd*?
By creating a symbolic link from **/etc/systemd/system/default.target** to one of the targets in **/lib/systemd/system**.
72
Where are the files for managing services located on a *systemd* system?
**/lib/systemd/system/\*.service** files represent control groups and are used for managing services. They are equivalent to **init** scripts in **/etc/rc.d/init.d**.

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