将用户添加到组

假设你有两个用户名为 chyingp 和 casper 的用户，并希望将它们添加到组 root 中。

usermod chyingp -a -G root
usermod casper -a -G root

这里是 -a，-G 的解释

-a, --append
Add the user to the supplementary group(s). Use only with the -G option.
-G, --groups GROUP1[,GROUP2,...[,GROUPN]]]
A list of supplementary groups which the user is also a member of. Each group is separated from the next by
a comma, with no intervening whitespace. The groups are subject to the same restrictions as the group given
with the -g option.

If the user is currently a member of a group which is not listed, the user will be removed from the group.
This behaviour can be changed via the -a option, which appends the user to the current supplementary group
list.