Core functionality

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Core functionality

Example Configuration
Directives
accept_mutex
accept_mutex_delay
daemon
debug_connection
debug_points
env
error_log
events
include
load_module
lock_file
master_process
multi_accept
pcre_jit
pid
ssl_engine
ssl_object_cache_inheritable
stall_threshold
thread_pool
timer_resolution
use
user
worker_aio_requests
worker_connections
worker_cpu_affinity
worker_priority
worker_processes
worker_rlimit_core
worker_rlimit_nofile
worker_shutdown_timeout
working_directory

Example Configuration

user www www;
worker_processes 2;

error_log /var/log/nginx-error.log info;

events {
use kqueue;
worker_connections 2048;
}

...

Directives

Syntax:

accept_mutex on | off;

Default:

accept_mutex off;

Context:

events

If accept_mutex is enabled,
worker processes will accept new connections by turn.
Otherwise, all worker processes will be notified about new connections,
and if volume of new connections is low, some of the worker processes
may just waste system resources.

There is no need to enable accept_mutex
on systems that support the
EPOLLEXCLUSIVE flag (1.11.3) or
when using reuseport.

Prior to version 1.11.3, the default value was on.

Syntax:

accept_mutex_delay time;

Default:

accept_mutex_delay 500ms;

Context:

events

If accept_mutex is enabled, specifies the maximum time
during which a worker process will try to restart accepting new
connections if another worker process is currently accepting
new connections.

Syntax:

daemon on | off;

Default:

daemon on;

Context:

main

Determines whether nginx should become a daemon.
Mainly used during development.

Syntax:

debug_connection
address |
CIDR |
unix:;

Default:

—

Context:

events

Enables debugging log for selected client connections.
Other connections will use logging level set by the
error_log directive.
Debugged connections are specified by IPv4 or IPv6 (1.3.0, 1.2.1)
address or network.
A connection may also be specified using a hostname.
For connections using UNIX-domain sockets (1.3.0, 1.2.1),
debugging log is enabled by the “unix:” parameter.

events {
debug_connection 127.0.0.1;
debug_connection localhost;
debug_connection 192.0.2.0/24;
debug_connection ::1;
debug_connection 2001:0db8::/32;
debug_connection unix:;
...
}

For this directive to work, nginx needs to
be built with --with-debug,
see “A debugging log”.

Syntax:

debug_points abort | stop;

Default:

—

Context:

main

This directive is used for debugging.

When internal error is detected, e.g. the leak of sockets on
restart of working processes, enabling debug_points
leads to a core file creation (abort)
or to stopping of a process (stop) for further
analysis using a system debugger.

Syntax:

env variable[=value];

Default:

env TZ;

Context:

main

By default, nginx removes all environment variables inherited
from its parent process except the TZ variable.
This directive allows preserving some of the inherited variables,
changing their values, or creating new environment variables.
These variables are then:

inherited during a live upgrade
of an executable file;

used by the
ngx_http_perl_module module;

used by worker processes.
One should bear in mind that controlling system libraries in this way
is not always possible as it is common for libraries to check
variables only during initialization, well before they can be set
using this directive.
An exception from this is an above mentioned
live upgrade
of an executable file.

The TZ variable is always inherited and available to the
ngx_http_perl_module
module, unless it is configured explicitly.

Usage example:

env MALLOC_OPTIONS;
env PERL5LIB=/data/site/modules;
env OPENSSL_ALLOW_PROXY_CERTS=1;

The NGINX environment variable is used internally by nginx
and should not be set directly by the user.

Syntax:

error_log file [level]
[json];

Default:

error_log logs/error.log error;

Context:

main, http, mail, stream, server, location

Configures logging.
Several logs can be specified on the same configuration level (1.5.2).
If on the main configuration level writing a log to a file
is not explicitly defined, the default file will be used.

The first parameter defines a file that will store the log.

The special value stderr selects the standard error file.
Logging to syslog can be configured by specifying
the “syslog:” prefix.
Logging to a
cyclic memory buffer
can be configured by specifying the “memory:” prefix and
buffer size, and is generally used for debugging (1.7.11).

The second parameter determines the level of logging,
and can be one of the following:
debug, info, notice,
warn, error, crit,
alert, or emerg.
Log levels above are listed in the order of increasing severity.
Setting a certain log level will cause all messages of
the specified and more severe log levels to be logged.
For example, the default level error will
cause error, crit,
alert, and emerg messages
to be logged.
If this parameter is omitted then error is used.

For debug logging to work, nginx needs to
be built with --with-debug,
see “A debugging log”.

The json parameter (1.29.8)
enables writing a log in the JSON format,
with support for
context tags:

{
"level": "error",
"timestamp": "2026-05-13T10:30:15.042+00:00",
"pid": 12345, "tid": 12345, "cnum": 3,
"msg": "connect() failed",
"client": "192.168.1.10", "server": "example.com",
"request": "GET /api HTTP/1.1",
"upstream": "http://127.0.0.1:8080/api",
"errno": 111,
"errtext": "Connection refused"
}

A log entry cannot exceed 2 KB,
data beyond this limit is truncated to “truncated”:1.
Debug logging is not supported for JSON.

This parameter is available as part of our
commercial subscription.

The directive can be specified on the
stream level
starting from version 1.7.11,
and on the mail level
starting from version 1.9.0.

Syntax:

events { ... }

Default:

—

Context:

main

Provides the configuration file context in which the directives that
affect connection processing are specified.

Syntax:

include file | mask;

Default:

—

Context:

any

Includes another file, or files matching the
specified mask, into configuration.
Included files should consist of
syntactically correct directives and blocks.

Usage example:

include mime.types;
include vhosts/*.conf;

Syntax:

load_module file;

Default:

—

Context:

main

This directive appeared in version 1.9.11.

Loads a dynamic module.

Example:

load_module modules/ngx_mail_module.so;

Syntax:

lock_file file;

Default:

lock_file logs/nginx.lock;

Context:

main

nginx uses the locking mechanism to implement accept_mutex
and serialize access to shared memory.
On most systems the locks are implemented using atomic operations,
and this directive is ignored.
On other systems the “lock file” mechanism is used.
This directive specifies a prefix for the names of lock files.

Syntax:

master_process on | off;

Default:

master_process on;

Context:

main

Determines whether worker processes are started.
This directive is intended for nginx developers.

Syntax:

multi_accept on | off;

Default:

multi_accept off;

Context:

events

If multi_accept is disabled, a worker process
will accept one new connection at a time.
Otherwise, a worker process
will accept all new connections at a time.

The directive is ignored if kqueue
connection processing method is used, because it reports
the number of new connections waiting to be accepted.

Syntax:

pcre_jit on | off;

Default:

pcre_jit off;

Context:

main

This directive appeared in version 1.1.12.

Enables or disables the use of “just-in-time compilation” (PCRE JIT)
for the regular expressions known by the time of configuration parsing.

PCRE JIT can speed up processing of regular expressions significantly.

The JIT is available in PCRE libraries starting from version 8.20
built with the --enable-jit configuration parameter.
When the PCRE library is built with nginx (--with-pcre=),
the JIT support is enabled via the
--with-pcre-jit configuration parameter.

Syntax:

pid file;

Default:

pid logs/nginx.pid;

Context:

main

Defines a file that will store the process ID of the main process.

Syntax:

ssl_engine device;

Default:

—

Context:

main

Defines the name of the hardware SSL accelerator.

The module may be dynamically loaded by OpenSSL during configuration testing.

Syntax:

ssl_object_cache_inheritable on | off;

Default:

ssl_object_cache_inheritable on;

Context:

main

This directive appeared in version 1.27.4.

If enabled, SSL objects
(SSL certificates, secret keys, trusted CA certificates, CRL lists)
will be inherited across configuration reloads.

SSL objects loaded from a file are inherited
if the modification time and file index has not been changed
since the previous configuration load.
Secret keys specified as
engine:name:id are never inherited.
Secret keys specified as
data:value are always inherited.

SSL objects loaded from variables cannot be inherited.

Example:

ssl_object_cache_inheritable on;

http {
...
server {
...
ssl_certificate example.com.crt;
ssl_certificate_key example.com.key;
}
}

Syntax:

stall_threshold time;

Default:

stall_threshold 1000ms;

Context:

events

This directive appeared in version 1.29.0.

Allows overriding the default time threshold for the event loop iteration
before a stall is reported.
By default, a stall is reported
when an event loop iteration exceeds 1000ms.
If the timer_resolution directive is enabled,
the time threshold will be ignored.

This directive is available as part of our
commercial subscription.

Syntax:

thread_pool
name
threads=number
[max_queue=number];

Default:

thread_pool default threads=32 max_queue=65536;

Context:

main

This directive appeared in version 1.7.11.

Defines the name and parameters of a thread pool
used for multi-threaded reading and sending of files
without blocking
worker processes.

The threads parameter
defines the number of threads in the pool.

In the event that all threads in the pool are busy,
a new task will wait in the queue.
The max_queue parameter limits the number
of tasks allowed to be waiting in the queue.
By default, up to 65536 tasks can wait in the queue.
When the queue overflows, the task is completed with an error.

Syntax:

timer_resolution interval;

Default:

—

Context:

main

Reduces timer resolution in worker processes, thus reducing the
number of gettimeofday() system calls made.
By default, gettimeofday() is called each time
a kernel event is received.
With reduced resolution, gettimeofday() is only
called once per specified interval.

Example:

timer_resolution 100ms;

Internal implementation of the interval depends on the method used:

the EVFILT_TIMER filter if kqueue is used;

timer_create() if eventport is used;

setitimer() otherwise.

Syntax:

use method;

Default:

—

Context:

events

Specifies the connection processing
method to use.
There is normally no need to specify it explicitly, because nginx will
by default use the most efficient method.

Syntax:

user user [group];

Default:

user nobody nobody;

Context:

main

Defines user and group
credentials used by worker processes.
If group is omitted, a group whose name equals
that of user is used.

Syntax:

worker_aio_requests number;

Default:

worker_aio_requests 32;

Context:

events

This directive appeared in versions 1.1.4 and 1.0.7.

When using aio
with the epoll
connection processing method, sets the maximum number of
outstanding asynchronous I/O operations
for a single worker process.

Syntax:

worker_connections number;

Default:

worker_connections 512;

Context:

events

Sets the maximum number of simultaneous connections that
can be opened by a worker process.

It should be kept in mind that this number includes all connections
(e.g. connections with proxied servers, among others),
not only connections with clients.
Another consideration is that the actual number of simultaneous
connections cannot exceed the current limit on
the maximum number of open files, which can be changed by
worker_rlimit_nofile.

Syntax:

worker_cpu_affinity cpumask ...;
worker_cpu_affinity auto [cpumask];

Default:

—

Context:

main

Binds worker processes to the sets of CPUs.
Each CPU set is represented by a bitmask of allowed CPUs.
There should be a separate set defined for each of the worker processes.
By default, worker processes are not bound to any specific CPUs.

For example,

worker_processes 4;
worker_cpu_affinity 0001 0010 0100 1000;

binds each worker process to a separate CPU, while

worker_processes 2;
worker_cpu_affinity 0101 1010;

binds the first worker process to CPU0/CPU2,
and the second worker process to CPU1/CPU3.
The second example is suitable for hyper-threading.

The special value auto (1.9.10) allows
binding worker processes automatically to available CPUs:

worker_processes auto;
worker_cpu_affinity auto;

The optional mask parameter can be used to limit the CPUs
available for automatic binding:

worker_cpu_affinity auto 01010101;

The directive is only available on FreeBSD and Linux.

Syntax:

worker_priority number;

Default:

worker_priority 0;

Context:

main

Defines the scheduling priority for worker processes like it is
done by the nice command: a negative
number
means higher priority.
Allowed range normally varies from -20 to 20.

Example:

worker_priority -10;

Syntax:

worker_processes number | auto;

Default:

worker_processes 1;

Context:

main

Defines the number of worker processes.

The optimal value depends on many factors including (but not
limited to) the number of CPU cores, the number of hard disk
drives that store data, and load pattern.
When one is in doubt, setting it to the number of available CPU cores
would be a good start (the value “auto”
will try to autodetect it).

The auto parameter is supported starting from
versions 1.3.8 and 1.2.5.

Syntax:

worker_rlimit_core size;

Default:

—

Context:

main

Changes the limit on the largest size of a core file
(RLIMIT_CORE) for worker processes.
Used to increase the limit without restarting the main process.

Syntax:

worker_rlimit_nofile number;

Default:

—

Context:

main

Changes the limit on the maximum number of open files
(RLIMIT_NOFILE) for worker processes.
Used to increase the limit without restarting the main process.

Syntax:

worker_shutdown_timeout time;

Default:

—

Context:

main

This directive appeared in version 1.11.11.

Configures a timeout for a graceful shutdown of worker processes.
When the time expires,
nginx will try to close all the connections currently open
to facilitate shutdown.

Syntax:

working_directory directory;

Default:

—

Context:

main

Defines the current working directory for a worker process.
It is primarily used when writing a core-file, in which case
a worker process should have write permission for the
specified directory.