How to get the crumb of jenkins

I am now working on the secondary development of jenkins. I need to create a credentials, when adding a slave node in jenkins, but I need to provide crumb, when creating it through a http request. Do you know how to get crumb? Try curl-s" http://user:token@jenkins_server:8080/crumbIssuer/api/xml?xpath=concat(//crumbRequestField,":",//crumb)" this method is not successful, do you know any other methods? Thank you

Mar.02,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e546e1-452c0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e546e1-452c0.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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