2018年8月1日 星期三

[Linux 常見問題] Does curl have a timeout?

Source From Here 
Question 
So far I couldn't find anything really, but is it true that curl doesn't really time out at all? 
# curl http://localhost/testdir/image.jpg

Will curl always wait (or is it depending on configuration) or is there any sort of timeout? 

How-To 
curl has two options: --connect-timeout and --max-time. Quoting from the manpage: 
  1. --connect-timeout   
  2.     Maximum  time  in  seconds  that you allow the connection to the  
  3.     server to take.  This only limits  the  connection  phase,  once  
  4.     curl has connected this option is of no more use.  Since 7.32.0,  
  5.     this option accepts decimal values, but the actual timeout  will  
  6.     decrease in accuracy as the specified timeout increases in deci‐  
  7.     mal precision. See also the -m, --max-time option.  
  8.   
  9.     If this option is used several times, the last one will be used.  
and 
  1. -m, --max-time   
  2.     Maximum  time  in  seconds that you allow the whole operation to  
  3.     take.  This is useful for preventing your batch jobs from  hang‐  
  4.     ing  for  hours due to slow networks or links going down.  Since  
  5.     7.32.0this option accepts decimal values, but the actual time‐  
  6.     out will decrease in accuracy as the specified timeout increases  
  7.     in decimal precision.  See also the --connect-timeout option.  
  8.   
  9.     If this option is used several times, the last one will be used.  
Defaults 
Here (on Debian) it stops trying to connect after 2 minutes, regardless of the time specified with --connect-timeout and although the default connect timeout value seems to be 5 minutes according to the DEFAULT_CONNECT_TIMEOUT macro in lib/connect.h. A default value for --max-time doesn't seem to exist, making curl wait forever for a response if the initial connect succeeds. 

What to use? 
You are probably interested in the latter option, --max-time. For your case set it to 900 (15 minutes). 

Specifying option --connect-timeout to something like 60 (one minute) might also be a good idea. Otherwise curl will try to connect again and again, apparently using some backoff algorithm.

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