Add a user to a user group in Linux)

Add a user to a user group in Linux. do not directly use usermod-GgroupA to leave other user groups, it is only a member of the groupA user group. -A option should be added: usermod... add a user to a user group in Linux. do not directly use usermod-G groupA to leave other user groups, it is only a member of the groupA user group. -A option should be added: usermod-a-G groupA user (FC4: usermod-G groupA, groupB, groupC user)-a represents append, that is, add yourself to the groupA user group without leaving other user groups. Options:-c, -- comment COMMENT new value of the GECOS field-d, -- home HOME_DIR new home directory for the user account-e, -- expiredate EXPIRE_DATE set account expiration date to EXPIRE_DATE-f, -- inactive INACTIVE set password inactive after expiration to INACTIVE-g, -- gid GROUP force use GROUP as new primary group-G, -- groups GROUPS new list of supplementary GROUPS-a, -- append the user to the supplemental GROUPS mentioned by the-G option without removing him/her from other groups-h, -- help display this help message and exit-l, -- login NEW_LOGIN new value of the login name-L, -- lock the user account-m, -- move-home move contents of the home directory to the new location (use only with-d)-o, -- non-unique allow using duplicate (non-unique) UID-p, -- password PASSWORD use encrypted password for the new password-s, -- shell SHELL new login shell for the user account-u, -- uid UID new UID for the user account-U, -- unlock the user account to view the user's group command: $ groups user or view the file: $ cat/etc/group