Dependencies

NGINX has a small footprint of third-party dependencies. Most are detected at configure time; missing ones simply disable the corresponding feature.

Required (for a useful build)

Dependency	Used by	Header probe (auto/lib/...)	Notes
PCRE or PCRE2	rewrite, map, regex location, if	auto/lib/pcre/conf	PCRE2 preferred. Without it: no regex anywhere in the config.
zlib	gzip, gunzip, gzip_static filters	auto/lib/zlib/conf	Without it: no compression.
OpenSSL 1.1.1+	TLS, HTTP/2 ALPN, HTTP/3, QUIC	auto/lib/openssl/conf	Or BoringSSL / LibreSSL with the appropriate compat shim. For QUIC: see ngx_event_quic_openssl_compat.c.

Optional

Dependency	Used by	Configure flag
libxslt	ngx_http_xslt_filter_module	--with-http_xslt_module[=dynamic]
libgd	ngx_http_image_filter_module	--with-http_image_filter_module
libgeoip	ngx_http_geoip_module, ngx_stream_geoip_module	--with-http_geoip_module
Perl	ngx_http_perl_module	--with-http_perl_module[=dynamic]
libatomic_ops	Atomic ops on platforms without GCC builtins	--with-libatomic[=DIR]

Bundled (no external dependency)

The codebase contains its own implementations of:

• MD5 — src/core/ngx_md5.{c,h} (used unless OpenSSL provides one)
• SHA-1 — src/core/ngx_sha1.{c,h} (fallback)
• MurmurHash — src/core/ngx_murmurhash.{c,h}
• CRC32 — src/core/ngx_crc32.{c,h}
• Static Huffman tables for HPACK — src/http/ngx_http_huff_decode.c, src/http/ngx_http_huff_encode.c
• QUIC transport — src/event/quic/
• QPACK — src/http/v3/ngx_http_v3_table.c
• Async DNS resolver — src/core/ngx_resolver.{c,h}

OS dependencies

auto/os/conf selects per-OS code based on uname. Key features it probes for:

Feature	Where used
epoll(2)	Linux event backend
kqueue(2)	FreeBSD / macOS event backend
eventfd(2)	Linux AIO + thread-pool wakeup
io_setup(2) (libaio)	aio directive on Linux
signalfd(2)	Optional in some signal paths
SO_REUSEPORT	listen ... reuseport;
EPOLLEXCLUSIVE	Thundering-herd-free accept on Linux
accept4(2)	Combine accept + non-blocking flag
sendfile(2)	Static file response path
splice(2)	Some upstream-to-client paths
tee(2)	Tee in some pipe paths
TCP_FASTOPEN	listen ... fastopen=N;
IP_BIND_ADDRESS_NO_PORT	Outgoing connection optimization
eBPF (libbpf-style)	QUIC reuseport (Linux)
setaffinity family	worker_cpu_affinity

Reading nginx -V

The -V output reports the exact set of dependencies the binary was built against:

$ nginx -V
nginx version: nginx/1.31.0
built by gcc 13.2.0 (Ubuntu 13.2.0-23ubuntu4)
built with OpenSSL 3.4.0 22 Oct 2025
TLS SNI support enabled
configure arguments: --with-http_ssl_module --with-http_v2_module ...

The list of configure arguments is identical to what was passed to ./auto/configure. This is the most reliable way to know what's in any given build.

Build-time detection

auto/feature is the helper that compiles small C snippets to detect a feature. Each auto/lib/<name>/conf script does roughly:

1. Try the system path; if headers + library exist, set NGX_HAVE_<name> and link flags.
2. If not, try the user-supplied --with-<name>=DIR.
3. If still nothing, optionally fall back to a bundled copy (zlib, PCRE) or fail (OpenSSL when SSL was requested).

License compatibility

NGINX is 2-clause BSD. All bundled algorithms (MD5, SHA-1, MurmurHash, etc.) are public-domain or BSD-licensed. The dependencies above are all MIT/BSD/Apache/dual-licensed, except libgd and libgeoip which carry their own permissive licenses.

The Perl XS module's binding code is BSD; embedding Perl pulls in Perl's licensing for that build configuration.