A full sp_sysmon report contains hundreds of lines of output. Use isql input and output redirect flags to save the output to a file. For example, if you create a file named sysmon_in that contains this command to run sp_sysmon for 10 seconds:
sp_sysmon '00:00:10' go
Use the isql -o parameter to pipe the output to a file named sysmon_out:
$SYBASE/$SYBASE_OCS/bin/isql -Usa -P -Sbig_server -isysmon_in -osysmon_out
See Utility Programs Guide for more information on isql.