Membership in the operating system group designated as the OSASM group provides operating system authentication for the SYSASM system privilege. OSASM is provided exclusively for Oracle ASM. Initially, only the user that installs ASM is a member of the OSASM group, if you use a separate operating system group for that privilege. However, you can add other users. Members of the OSASM group are authorized to connect using the SYSASM privilege and have full access to Oracle ASM, including administrative access to all disk groups that are managed by that Oracle ASM instance.
On Linux and UNIX systems, dba is the default operating system group designated as OSASM, OSOPER, and OSDBA for Oracle ASM.
On Windows systems, ORA_ASMADMIN, ORA_ASMDBA, and ORA_ASMOPER are the operating system groups designated for OSASM, OSDBA and OSOPER respectively for Oracle ASM.
SQL*Plus commands, ASMCMD commands, and ASMCA use operating system authentication.
Oracle Database Administrator's Guide for more information about using operating system authentication
Oracle Grid Infrastructure Installation Guide for information about installation of the Oracle Grid Infrastructure
Oracle Database Installation Guide for your specific operating system for information about default operating system groups