curl ootw: –retry-max-time

Previous command line options of the week.

--retry-max-time has no short option alternative and it takes a numerical argument stating the time in seconds. See below for a proper explanation for what that time is.

Retrying

curl supports retrying of operations that failed due to “transient errors”, meaning that if the error code curl gets signals that the error is likely to be temporary and not the fault of curl or the user using curl, it can try again. You enable retrying with --retry [tries] where you tell curl how many times it should retry. If it reaches the maximum number of retries with a successful transfer, it will return error.

A transient error can mean that the server is temporary overloaded or similar, so when curl retries it will by default wait a short while before doing the next “round”. By default, it waits one second on the first retry and then it doubles the time for every new attempt until the waiting time reaches 10 minutes which then is the max waiting time. A user can set a custom delay between retries with the --retry-delay option.

Transient errors

Transient errors mean either: a timeout, an FTP 4xx response code or an HTTP 408 or 5xx response code. All other errors are non-transient and will not be retried with this option.

Retry no longer than this

Retrying can thus go on for an extended period of time, and you may want to limit for how long it will retry if the server really doesn’t work. Enter --retry-max-time.

It sets the maximum number of seconds that are allowed to have elapsed for another retry attempt to be started. If you set the maximum time to 20 seconds, curl will only start new retry attempts within a twenty second period that started before the first transfer attempt.

If curl gets a transient error code back after 18 seconds, it will be allowed to do another retry and if that operation then takes 4 seconds, there will be no more attempts but if it takes 1 second, there will be time for another retry.

Of course the primary --retry option sets the number of times to retry, which may reach the end before the maximum time is met. Or not.

Retry-After:

Since curl 7.66.0 (September 2019), the server’s Retry-After: HTTP response header will be used to figure out when the subsequent retry should be issued – if present. It is a generic means to allow the server to control how fast clients will come back, so that the retries themselves don’t become a problem that causes more transient errors…

–retry-connrefused

In curl 7.52.0 curl got this additional retry switch that adds “connection refused” as a valid reason for doing a retry. If not used, a connection refused is not considered a transient error and will cause a regular error exit code.

Related options

--max-time limits the entire time allowed for an operation, including all retry attempts.

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