curl_global_trace(3) Library Functions Manual curl_global_trace(3)
NAME
curl_global_trace - log configuration
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_global_trace(const char *config);
DESCRIPTION
This function configures the logging behavior to make some parts of curl
more verbose or silent than others.
This function may be called during the initialization phase of a pro-
gram. It does not have to be. It can be called several times even, pos-
sibly overwriting settings of previous calls.
Calling this function after transfers have been started is undefined. On
some platforms/architectures it might take effect, on others not.
This function is thread-safe since libcurl 8.3.0 if curl_version_info(3)
has the CURL_VERSION_THREADSAFE feature bit set (most platforms).
If this is not thread-safe, you must not call this function when any
other thread in the program (i.e. a thread sharing the same memory) is
running. This does not just mean no other thread that is using libcurl.
Because curl_global_init(3) may call functions of other libraries that
are similarly thread unsafe, it could conflict with any other thread
that uses these other libraries.
If you are initializing libcurl from a Windows DLL you should not ini-
tialize it from DllMain or a static initializer because Windows holds
the loader lock during that time and it could cause a deadlock.
The config string is a list of comma-separated component names. Names
are case-insensitive and unknown names are ignored. The special name
"all" applies to all components. Names may be prefixed with '+' or '-'
to enable or disable detailed logging for a component.
The list of component names is not part of curl's public API. Names may
be added or disappear in future versions of libcurl. Since unknown names
are silently ignored, outdated log configurations does not cause errors
when upgrading libcurl. Given that, some names can be expected to be
fairly stable and are listed below for easy reference.
Note that log configuration applies only to transfers where debug log-
ging is enabled. See CURLOPT_VERBOSE(3) or CURLOPT_DEBUGFUNCTION(3) on
how to control that.
TRACE COMPONENTS
tcp Tracing of TCP socket handling: connect, sends, receives.
ssl Tracing of SSL/TLS operations, whichever SSL backend is used in
your build.
ftp Tracing of FTP operations when this protocol is enabled in your
build.
http/2 Details about HTTP/2 handling: frames, events, I/O, etc.
http/3 Details about HTTP/3 handling: connect, frames, events, I/O etc.
http-proxy
Involved when transfers are tunneled through an HTTP proxy.
"h1-proxy" or "h2-proxy" are also involved, depending on the HTTP
version negotiated with the proxy.
In order to find out all components involved in a transfer, run
it with "all" configured. You can then see all names involved in
your libcurl version in the trace.
dns Tracing of DNS operations to resolve hostnames and HTTPS records.
lib-ids
Adds transfer and connection identifiers as prefix to every call
to CURLOPT_DEBUGFUNCTION(3). The format is [n-m] where n is the
identifier of the transfer and m is the identifier of the connec-
tion. A literal x is used for internal transfers or when no con-
nection is assigned.
For example, [5-x] is the prefix for transfer 5 that has no con-
nection. The command line tool curluses the same format for its
--trace-ids option.
lib-ids is intended for libcurl applications that handle multiple
transfers but have no own way to identify in trace output which
transfer a trace event is connected to.
doh Former name for DNS-over-HTTP operations. Now an alias for dns.
multi Traces multi operations managing transfers' state changes and
sockets poll states.
read Traces reading of upload data from the application in order to
send it to the server.
ssls Tracing of SSL Session handling, e.g. caching/import/export.
smtp Tracing of SMTP operations when this protocol is enabled in your
build.
write Traces writing of download data, received from the server, to the
application.
ws Tracing of WebSocket operations when this protocol is enabled in
your build.
TRACE GROUPS
Besides the specific component names there are the following group names
defined:
all
network
All components involved in bare network I/O, including the SSL
layer.
All components that your libcurl is built with.
protocol
All components involved in transfer protocols, such as 'ftp' and
'http/2'.
proxy All components involved in use of proxies.
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
/* log details of HTTP/2 and SSL handling */
curl_global_trace("http/2,ssl");
/* log all details, except SSL handling */
curl_global_trace("all,-ssl");
}
Below is a trace sample where "http/2" was configured. The trace output
of an enabled component appears at the beginning in brackets.
* [HTTP/2] [h2sid=1] cf_send(len=96) submit https://example.com/
...
* [HTTP/2] [h2sid=1] FRAME[HEADERS]
* [HTTP/2] [h2sid=1] 249 header bytes
...
AVAILABILITY
Added in curl 8.3.0
RETURN VALUE
If this function returns non-zero, something went wrong and the configu-
ration may not have any effects or may only been applied partially.
SEE ALSO
curl_global_init(3), libcurl(3)
libcurl 2026-07-12 curl_global_trace(3)
Generated by dwww version 1.16 on Sat Oct 3 04:23:25 CEST 2026.