Linkage Indexes are reserved via LXRES, using either the LXLIST or ELXLIST keyword. ELXLIST is properly documented as relating to "extended linkage index".
I don't know why the OP had difficulty locating that information. Searching the z/OS documentation for extended linkage index had the expected hits. Adam J's response describes just what the OP did wrong. Peter Relson z/OS Core Technology Design ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN