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COAP-SERVER(5) coap-server Manual COAP-SERVER(5) NAME coap-server, coap-server-gnutls, coap-server-mbedtls, coap-server-openssl, coap-server-notls - CoAP Server based on libcoap SYNOPSIS coap-server [-a priority] [-b max_block_size] [-d max] [-e] [-f scheme://addr[:port] [-g group] [-l loss] [-p port] [-q tls_en- gine_conf_file] [-r] [-t] [-v num] [-w [port][,secure_port]] [-A address] [-E oscore_conf_file[,seq_file]] [-G group_if] [-L value] [-N] [-P scheme://addr[:port],[name1[,name2..]]] [-T max_token_size] [-U type] [-V num] [-X size] [[-h hint] [-i match_identity_file] [-k key] [-s match_psk_sni_file] [-u user] [-2]] [[-c certfile] [-j keyfile] [-n] [-C cafile] [-J pkcs11_pin] [-M rpk_file] [-R trust_casfile] [-S match_pki_sni_file]] For coap-server versions that use libcoap compiled for different (D)TLS li- braries, coap-server-notls, coap-server-gnutls, coap-server-openssl, coap-server-mbedtls or coap-server-tinydtls may be available. Otherwise, coap-server uses the default libcoap (D)TLS support. DESCRIPTION coap-server is an example server for the 'Constrained Application Protocol` (RFC 7252). OPTIONS - GENERAL -a priority Send logging output to syslog at priority (0-7) level. -b max_block_size Maximum block size server supports (16, 32, 64, 128, 256, 512 or 1024) in bytes. -d max Enable support for creation of dynamic resources when doing a PUT up to a limit of max. If max is reached, a 4.06 code is returned until one of the dynamic resources has been deleted. -e Echo back the data sent with a PUT. -f scheme://address[:port] Act as a reverse proxy where scheme, address, optional port define how to connect to the internal server. Scheme is one of coap, coaps, coap+tcp, coaps+tcp, coap+ws, and coaps+ws. http(s) is not currently supported. This option can be repeated to provide multiple internal servers that are round-robin load balanced. -g group Join specified multicast group on start up. Note: DTLS over multicast is not currently supported. -l list Fail to send some datagrams specified by a comma separated list of num- bers or number ranges (debugging only). -l loss% Randomly failed to send datagrams with the specified probability - 100% all datagrams, 0% no datagrams (debugging only). -p port The port on the given address will be listening for incoming connec- tions. If (D)TLS is supported, then port + 1 will also be listened on for (D)TLS connections. The default port is 5683 if not given any other value. -q tls_engine_conf_file tls_engine_conf_file contains TLS ENGINE configuration. Only OpenSSL is currently supported. See coap-tls-engine-conf(5) for definitions. -r Enable multicast per resource support. If enabled, only /, /async and /.well-known/core are enabled for multicast requests support, otherwise all resources are enabled. -t Track resource's observe values so observe subscriptions can be main- tained over a server restart. Note: Use kill SIGUSR2 <pid> for con- trolled shutdown. -v num The verbosity level to use (default 4, maximum is 8) for general CoAP logging. -w [port][,secure_port] Enable WebSockets support support on port (WS) and/or secure_port (WSS), comma separated. -A address The local address of the interface which the server has to listen on. -E oscore_conf_file[,seq_file] oscore_conf_file contains OSCORE configuration. See coap-oscore-conf(5) for definitions. Optional seq_file (which is created if needed) is used to save the current transmit sequence number, so on server restart se- quence numbers continue to increase and are not reset to prevent anti-replay mechanisms being triggered. -G group_if Use this interface for listening for the multicast group. This can be different from the implied interface if the -A option is used. -L value Sum of one or more COAP_BLOCK_* flag values for different block han- dling methods. Default is 1 (COAP_BLOCK_USE_LIBCOAP). COAP_BLOCK_USE_LIBCOAP 1 COAP_BLOCK_SINGLE_BODY 2 COAP_BLOCK_TRY_Q_BLOCK 4 COAP_BLOCK_STLESS_BLOCK2 64 COAP_BLOCK_NOT_RANDOM_BLOCK1 128 -N Send NON-confirmable message for "observe" responses. If option -N is not specified, a confirmable response will be sent. Even if set, every fifth response will still be sent as a confirmable response (RFC 7641 requirement). -P scheme://address[:port],[name1[,name2[,name3..]]] Scheme, address, optional port of how to connect to the next proxy server and zero or more names (comma separated) that this proxy server is known by. The , (comma) is required. If there is no name1 or if the hostname of the incoming proxy request matches one of these names, then this server is considered to be the final endpoint. If scheme://ad- dress[:port] is not defined before the leading , (comma) of the first name, then the ongoing connection will be a direct connection. Scheme is one of coap, coaps, coap+tcp, coaps+tcp, coap+ws, and coaps+ws. http and https not currently supported. This option can be repeated to pro- vide multiple upstream servers that are round-robin load balanced. -T max_token_size Set the maximum token length (8-65804). -U type Treat address defined by -A as a Unix socket address. Type is coap (us- ing datagram), coap+tcp (using stream), coaps (DTLS using datagram) or coaps+tcp (TLS using stream). -V num The verbosity level to use (default 3, maximum is 7) for (D)TLS library logging. -X size Maximum message size to use for TCP based connections (default is 8388864). Maximum value of 2^32 -1. OPTIONS - PSK (If supported by underlying (D)TLS library) -h hint Identity Hint to send. Default is CoAP. Zero length is no hint. -i match_identiity_file This is a file that contains one or more lines of Identity Hints and (user) Identities to match for a different new Pre-Shared Key (PSK) (comma separated) to be used. E.g., per line hint_to_match,identity_to_match,use_key A line that starts with # is treated as a comment. Note: -k still needs to be defined for the default case. Note: A match using the -s option may mean that the current Identity Hint is different to that defined by -h. -k key Pre-shared key to use for inbound connections. This cannot be empty if defined. If the key begins with 0x, then the hex text (two [0-9a-f] per byte) is converted to binary data. Note: if -c cafile is defined, you need to define -k key as well to have the server support both PSK and PKI. -s match_psk_sni_file This is a file that contains one or more lines of received Subject Name Identifier (SNI) to match to use a different Identity Hint and associ- ated Pre-Shared Key (PSK) (comma separated) instead of the -h hint and -k key options. E.g., per line sni_to_match,use_hint,with_key Note: -k key still needs to be defined for the default case if there is not a match. Note: The associated Pre-Shared Key will get updated if there is also a -i match. The update checking order is -s followed by -i. -u user User identity for pre-shared key mode (only used if option -P is set). -2 Use EC-JPAKE negotiation (if supported). OPTIONS - PKI (If supported by underlying (D)TLS library) Note: If any one of certfile, keyfile or cafile is in PKCS11 URI naming format (pkcs11: prefix), then any remaining non PKCS11 URI file definitions have to be in DER, not PEM, format. Otherwise all of certfile, keyfile or cafile are in PEM format. -c certfile PEM file or PKCS11 URI for the certificate. The private key can also be in the PEM file, or has the same PKCS11 URI. If not, the private key is defined by -j keyfile. Note: if -k key is defined, you need to define -c certfile as well to have the server support both PSK and PKI. -j keyfile PEM file or PKCS11 URI for the private key for the certificate in -c certfile if the parameter is different from certfile in -c certfile. -n Disable remote peer certificate checking. This gives clients the abil- ity to use PKI, but without any defined certificates. -C cafile PEM file or PKCS11 URI that contains a list of one or more CAs that are to be passed to the client for the client to determine what client cer- tificate to use. Normally, this list of CAs would be the root CA and any intermediate CAs. Ideally the server certificate should be signed by the same CA so that mutual authentication can take place. The con- tents of cafile are added to the trusted store of root CAs. Using the -C or -R options will trigger the validation of the client certificate unless overridden by the -n option. -J pkcs11_pin The user pin to unlock access to the PKCS11 token. -M Raw Public Key (RPK) PEM file or PKCS11 URI that contains both PUBLIC KEY and PRIVATE KEY or just EC PRIVATE KEY. (GnuTLS and TinyDTLS(PEM) support only). -C cafile or -R trust_casfile are not required. -R trust_casfile PEM file containing the set of trusted root CAs that are to be used to validate the client certificate. Alternatively, this can point to a di- rectory containing a set of CA PEM files. The -C cafile CA does not have to be in this list and is trusted for the validation. Using -R trust_casfile disables common CA mutual authentication which can only be done by using -C cafile. Using the -C or -R options will trigger the validation of the client certificate unless overridden by the -n op- tion. -S match_pki_sni_file This option denotes a file that contains one or more lines of Subject Name Identifier (SNI) to match for new certificate File and new CA File (comma separated) to be used. E.g., entry per line sni_to_match,new_cert_file,new_ca_file A line that starts with # is treated as a comment. Note: -c certfile and -C cafile still needs to be defined for the de- fault case EXAMPLES * Example coap-server -A ::1 Let the server listen on localhost (port 5683) for UDP/TCP. * Example coap-server -A ::1 -k mysecretKey -h myhint Let the server listen on localhost (port 5683 for UDP/TCP and port 5684 for DTLS/TLS) with the server set up for PSK authentication if the client uses coaps:// or coaps+tcp://. * Example coap-server -A ::1 -k mysecretKey -h myhint -p 13011 The same, except the UDP/TCP listening port is 13011 and the DTLS/TLS lis- tening port is 13012 (and not the default ports 5683 and 5684). * Example coap-server -A 2001:db8:81a8:0:6ef0:dead:feed:beef -v 5 The listening address is set to 2001:db8:81a8:0:6ef0:dead:feed:beef and the verbosity level is set to 5. * Example coap-server -A 2001:db8:81a8:0:6ef0:dead:feed:beef -g FF02::FD Set listening address to 2001:db8:81a8:0:6ef0:dead:feed:beef and join the All CoAP Nodes multicast group FF02::FD. * Example coap-server -P, -A ::1 Let the server listen on localhost (port 5683) for UDP/TCP, as well as ac- cept any CoAP proxy requests and directly respond to them. * Example coap-server -P coap://upstream-proxy, -A ::1 Let the server listen on localhost (port 5683) for UDP/TCP, and then open an upstream coap session to upstream-proxy for proxying onwards the CoAP client's request. FILES There are no configuration files. EXIT STATUS 0 Success 1 Failure (syntax or usage error; configuration error; document process- ing failure; unexpected error) SEE ALSO coap-client(5) and coap-oscore-conf(5) BUGS Please raise an issue on GitHub at https://github.com/obgm/libcoap/issues to report any bugs. Please raise a Pull Request at https://github.com/obgm/libcoap/pulls for any fixes. AUTHORS The libcoap project <libcoap-developers@lists.sourceforge.net> coap-server 4.3.5 08/02/2026 COAP-SERVER(5)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS - GENERAL | OPTIONS - PSK | OPTIONS - PKI | EXAMPLES | FILES | EXIT STATUS | SEE ALSO | BUGS | AUTHORS
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