z/OS UNIX REXX exec

As documented in Using REXX and z/OS UNIX System Services (SA22-7806), z/OS® UNIX offers the seteuid SYSCALL command to set the effective UID of the current process. There are few things to keep in mind when using the seteuid command.
  • The seteuid command uses the z/OS UNIX UID, not the MVS™ user ID. You must first determine the UID of the target user ID, which can be done with the getpwnam SYSCALL command.
  • The user ID executing the seteuid command must have READ permission to the BPX.SRV.<userid> profile in the SURROGAT class of your security product to be able to switch to the user ID identified by <userid> without specifying a password. Note that when multiple user IDs share the same UID, there is no way to determine which one of the user IDs will be checked.
/* rexx */
myID='ibmuser'
say userid()
address SYSCALL 'getpwnam' myID 'pw.'
say pw.1 pw.2 pw.3 pw.4 pw.5
address SYSCALL 'seteuid' pw.2  /* PW_UID = 2 */
say retval errno errnojr
say userid()

This sample logon exit, executed by the started task user ID, will result in the following console messages:

+FEK910I LOGON EXIT: invoking logon processing exit in thread 515
+FEK910I LOGON EXIT: STCRSE
+FEK910I LOGON EXIT: IBMUSER  1 0 / /bin/sh
+FEK910I LOGON EXIT: 0 0 0
+FEK910I LOGON EXIT: IBMUSER
+FEK910I LOGON EXIT: completed logon processing exit in thread 515