In this section, we will take a closer look
at the base modules. We are particularly interested in answering two
questions what are base modules and what directives are made available.
What are base modules?
The base modules offer directives that allow you to
define parameters of the basic functionality of Nginx. They cannot be
disabled at compile time; as a result, the directives and blocks they
offer are always available. Three base modules are distinguished:
These modules offer a large range of directives; we will be detailing them individually with their syntaxes and default values.
Nginx process architecture
Before we start detailing the basic configuration
directives, it's necessary to understand the process architecture, that
is, how Nginx works behind the scenes. Although the application comes as
a simple binary file, (apparently lightweight background process) the
way it functions at runtime is rather intricate.
At the very moment of starting Nginx, one unique process exists in memory the Master Process. It is launched with the current user and group permissions usually root/root if the service is launched at boot time by an init script. The master process itself does not process any client request; instead, it spawns processes that do the Worker Processes,
which are affected to a customizable user and group. From the
configuration file, you are able to define the amount of worker
processes, the maximum connections per worker process, and more.
Core module directives
Below is the list of directives made available by
the Core module. Most of these directives must be placed at the root of
the configuration file and can only be used once. However, some of them
are valid in multiple contexts. If that is the case, the list of valid
contexts is mentioned below the directive name.root of the configuration file and can only be used once.
|
Name and context
|
Syntax and description
|
|---|
|
daemon
|
Accepted values: on or off
Syntax:
daemon on;
Default value: on
Enables or disables daemon mode. If you disable it, the program will not
be started in the background; it will stay in the foreground when
launched from the shell.
|
|
debug_points
|
Accepted values: stop or abort
Syntax:
debug_points stop;
Default value: None.
Activates debug points in Nginx. Use stop to interrupt the application when a debug point comes about in order to attach a debugger. Use abort to abort the debug point and create a core dump file.
To disable this option, simply do not use the directive.
|
|
env
|
Syntax:
env MY_VARIABLE;
env MY_VARIABLE=my_value;
Lets you (re)define environment variables.
|
|
error_log
Context: main, http, server, and location
|
Syntax:
error_log /file/path level;
Default value: logs/error.log error.
Where level is one of the following values: debug, info, notice, warn, error, and crit (from most to least detailed: debug provides frequent log entries, crit only reports critical errors).
Enables error logging at different levels: Application, HTTP server, virtual host, and virtual host directory.
By redirecting the log output to /dev/null, you can disable error logging. Use the following directive at the root of the configuration file:
error_log /dev/null crit;
|
|
lock_file
|
Syntax: File path
lock_file logs/nginx.lock;
Default value: Defined at compile time
Use a lock file for mutual exclusion. Disabled by default, unless you enabled it at compile time.
|
|
log_not_found
Context: main, http, server, and location
|
Accepted values: on or off
log_not_found on;
Default value: on
Enables or disables logging of 404 not found HTTP errors. If your logs get filled with 404 errors due to missing favicon.ico or robots.txt files, you might want to turn this off.
|
|
master_process
|
Accepted values: on or off
master_process on;
Default value: on
If enabled, Nginx will start multiple processes: A main process (the
master process) and worker processes. If disabled, Nginx works with a
unique process. This directive should be used for testing purposes only
as it disables the master process clients thus cannot connect to your
server.
|
|
pid
|
Syntax: File path
pid logs/nginx.pid;
Default value: Defined at compile time.
Path of the pid file for the Nginx daemon. The default value can be configured at compile time.
|
|
ssl_engine
|
Syntax: Character string
ssl_engine enginename;
Default value: None
Where enginename is the name of an available
hardware SSL accelerator on your system. To check for available
hardware SSL accelerators, run this command from the shell:
openssl engine -t
|
|
thread_stack_size
|
Syntax: Numeric (size)
thread_stack_size 1m;
Default value: None
Defines the size of thread stack; please refer to the worker_threads directive below
|
|
timer_resolution
|
Syntax: Numeric (time)
timer_resolution 100ms;
Default value: None
Controls the interval between system calls to gettimeofday() to synchronize the internal clock. If this value is not specified, the clock is refreshed after each kernel event notification.
|
|
user
|
Syntax:
user username groupname;
user username;
Default value: Defined at compile time. If still undefined, the user and group of the Nginx master process are used.
Lets you define the user account and optionally the user group used for starting the Nginx worker processes.
|
|
worker_threads
|
Syntax: Numeric
worker_threads 8;
Default value: None
Defines the amount of threads per worker process.
Warning! Threads are disabled by default. The author stated that "the code is currently broken".
|
|
worker_cpu_affinity
|
Syntax:
worker_cpu_affinity 1000 0100 0010 0001;
worker_cpu_affinity 10 10 01 01;
worker_cpu_affinity;
Default value: None
This directive works in conjunction with worker_processes. It lets you affect worker processes to CPU cores.
There are as many series of digit blocks as worker processes; there are as many digits in a block as your CPU has cores.
If you configure Nginx to use three worker processes,
there are three blocks of digits. For a dual-core CPU, each block has
two digits.
worker_cpu_affinity 01 01 10;
The first block (01) indicates that the first worker process should be affected to the second core.
The second block (01) indicates that the second worker process should be affected to the second core.
The third block (10) indicates that the third worker process should be affected to the first core.
Note that affinity is only recommended for multi-core CPUs, not for processors with hyper-treading or similar technologies.
|
|
worker_priority
|
Syntax: Numeric
worker_priority 0;
Default value: 0
Defines the priority of the worker processes, from -20 (highest) to 19 (lowest). The default value is 0. Note that kernel processes run at priority level -5, so it's not recommended that you set the priority to -5 or less.
|
|
worker_processes
|
Syntax: Numeric
worker_processes 4;
Default value: 1
Defines the amount of worker processes. Nginx offers
to separate the treatment of requests into multiple processes. The
default value is 1, but it's recommended to increase this value if your
CPU has more than one core.
Besides, if a process gets blocked due to slow I/O operations, incoming requests can be delegated to the other worker processes.
|
|
worker_rlimit_core
|
Syntax: Numeric (size)
worker_rlimit_core 100m;
Default value: None
Defines the size of core files per worker process.
|
|
worker_rlimit_nofile
|
Syntax: Numeric
worker_rlimit_nofile 10000;
Default value: None
Defines the amount of files a worker process may use simultaneously.
|
|
worker_rlimit_sigpending
|
Syntax: Numeric
worker_rlimit_sigpending 10000;
Default value: None
Defines the amount of signals that can be queued per user (user ID of
the calling process). If the queue is full, signals are ignored past
this limit.
|
|
working_directory
|
Syntax: Directory path
working_directory /usr/local/nginx/;
Default value: The prefix switch defined at compile time.
Working directory used for worker processes; only used to define the
location of core files. The worker process user account (user directive)
must have write permissions on this folder in order to be able to write
core files.
|
Events module
The Events module comes with directives that allow
you to configure network mechanisms. Some of the parameters have an
important impact on the application's performance.
All of the directives listed below must be placed in the events block, which is located at the root of the configuration file:
user nginx nginx;
master_process on;
worker_processes 4;
events
worker_connections 1024;
use epoll;
}
[...]
These directives cannot be placed elsewhere (if you do so, the configuration test will fail).
|
Directive name
|
Syntax and description
|
|---|
|
accept_mutex
|
Accepted values: on or off
accept_mutex on;
Default value: on
Enables or disables the use of an accept mutex (mutual exclusion) to open listening sockets.
|
|
accept_mutex_delay
|
Syntax: Numeric (time)
accept_mutex_delay 500ms;
Default value: 500 milliseconds
Defines the amount of time a worker process should wait before trying to
acquire the resource again. This value is not used if the accept_mutex directive is set to off.
|
|
connections
|
Replaced by worker_connections. This directive is now deprecated.
|
|
debug_connection
|
Syntax: IP address or CIDR block.
debug_connection 172.63.155.21;
debug_connection 172.63.155.0/24;
Default value: None.
Writes detailed logs for clients matching this IP
address or address block. The debug information is stored in the file
specified with the error_log directive, enabled with the debug level.
Note: Nginx must be compiled with the --debug switch in order to enable this feature.
|
|
multi_accept
|
Syntax: on or off
multi_accept off;
Default value: off
Defines whether or not Nginx should accept all incoming connections from the listening queue at once.
|
|
use
|
select: The default and standard module, it is used if the OS
does not support a more efficient one (it's the only available method
under Windows)
poll: It is automatically preferred over select, but not available on all systems
Accepted values: /dev/poll, epoll, eventport, kqueue, rtsig, or select
use kqueue;
Default value: Defined at compile time Selects
the event model among the available ones (the ones that you enabled at
compile time), though Nginx automatically selects the most appropriate
one. The supported models are:
kqueue: An efficient method for FreeBSD 4.1+, OpenBSD 2.9+, NetBSD 2.0, and MacOS X operating systems
epoll: An efficient method for Linux 2.6+ based operating systems
rtsig: Real time signals, available as of Linux 2.2.19, but
unsuited for high-traffic profiles as default system settings only allow
1,024 queued signals
/dev/poll: An efficient method for Solaris 7 11/99+, HP/UX 11.22+, IRIX 6.5.15+, and Tru64 UNIX 5.1A+ operating systems
eventport: An efficient method for Solaris 10, though a security patch is required
|
|
worker_connections
|
Syntax: Numeric
worker_connections 1024;
Default value: None
Defines the amount of connections that a worker process may treat simultaneously.
|
Configuration module
The Nginx Configuration module is a simple module
enabling file inclusions with the include directive, as previously
described in the Organization and inclusions section. The directive can be inserted anywhere in the configuration file and accepts a single parameter the file's path.
include /file/path.conf;
include sites/*.conf;
Note that if you do not specify an absolute path, the file path is relative to the configuration directory. By default, include sites/example.conf will include the following file:
/usr/local/nginx/conf/sites/example.conf.
