What is Curl?
Curl is an open-source command-line tool and cross-platform library (libcurl) for transferring data to and from a server. Curl supports all popular internet protocols, including HTTP and HTTPS. Developers use Curl to test APIs, automate tasks, and support SSL certificates and HTTP Cookies. Curl works on all modern platforms like Windows, Linux, and macOS.
What is Timeout?
The waiting time is called a timeout. Curl sends requests works over a network connection. The first step in getting a resource from a server is to connect to that server. Establishing a connection with a remote server may take some time, depending on network speed, network latency, and server load. Curl has default timeouts for connection and total request time, but we can specify our timeouts for each Curl command.
How to set a timeout for a Curl command?
To set a timeout for a Curl command, you can use the --connect-timeout parameter to set the maximum time in seconds that you allow Curl to connect to the server, or the --max-time (or -m) parameter for the total time in seconds that you authorize the whole operation.
What is --connect-timeout and how to use it?
The –connect-timeout parameter limits the amount of time Curl will spend trying to connect to the remote host. The connection timeout value is specified in seconds. If Curl cannot establish a connection within the specified interval, the command fails.
What is -max-time and how to use it?
The –max-time (or -m) parameter is the maximum time, in seconds, within which the entire operation must completed or be canceled. The --max-time option can prevent Curl from hanging when executing batch jobs on slow networks.
Curl Timeout Examples
In the following example, we set a connection timeout for the Curl command when sending a request to the ReqBin echo URL:
To limit the total time for the Curl command to ten seconds, we can use the --max-time option:
We can use both timeouts in one command:
You can use --speed-limit and --speed-time as timeout alternative
You can use the --speed-time and -speed-limit command-line options as an alternative to the fixed timeout. With these parameters, you can tell Curl to cancel a transmission if it falls below a certain speed and stays below that threshold for a certain amount of time. For example, if the baud rate falls below 5000 bytes per second for 15 seconds, Curl will stop this:
What is TCP Timeout?
TCP stands for Transmission Control Protocol. The TCP keepalive timeout specifies the interval during which a TCP connection checks to see if a Fiber Channel over IP (FCIP) link is up. This ensures that a link failure is detected quickly, even if the link is inactive. Curl enables TCP support by default. TCP keepalive is a feature that makes the TCP stack send a probe to the other side when there is no traffic to make sure it is still there and alive. Use --keepalive-time to specify how often you want the probe to be sent to the partner in whole seconds. The default is 60 seconds. Sometimes this probing interferes with what you are doing, and you can easily disable it with --no-keepalive.