Single-Computer Setup for iOS
When setting up a Jenkins master with the intention of building for iOS on the same computer, the Jenkins user that is created will not have a default keychain to start with, and this will break the build process. You have two options: You can either change the user that the Jenkins server runs as (see the Jenkins documentation for this), or you can create the default keychain for the Jenkins user.
Note: When creating .p12 files for a single-computer setup like this, keep in mind that the Jenkins user does not have access to the associated keys you have on other user accounts. These must be included in the .p12 files you export, or placed in the JenkinsDefault keychain by hand.