changing workspace of jenkins in linux
Try
ps aux |grep jenkinsto see what user the process has. On Linux, jenkins uses the JENKINS_USER variable to define what user it should run as. For a standard Ubuntu package install, the config file in /etc/default/jenkins specifies the user in the JENKINS_USER variable.
In the same config file, you can also specify the default workspace location using JENKINS_HOME. Make sure that is owned by the user you specified in JENKINS_USER to have Jenkins access files.
For slave nodes, specify the default workspace on the slave machine in the slave configuration under Manage Jenkins > Manage Nodes > > Configure > Remote FS root. Again, this should have read/write/execute permissions for the JENKINS_USER user.