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To create and add a new user, use the "useradd" command By specifying a user name as an argument to the command, a user will be created. The user directory will be created under the /home directory, and the group name will be the same as the user name.

To create and add a new group, use the "groupadd" command. Information about groups is described in /etc/group and can be edited, but it is better to edit the group information with the vigr command instead of directly editing the "/etc/group" file.

Check the group in /etc/passwd and /etc/group (check the gid) Users always belong to a group, and the group described in the /etc/passwd and /etc/group files is the primary group. The gid (group ID) is stored in the /etc/passwd and /etc/group files

Group information in Linux is stored in the "/etc/group" file, which has the following notation tama:x:500: From left to right, tama is the group name, X is the password (when it says X, it is written in the /etc/gshadow file). 500 is the GID. To make a user belong to multiple groups, edit the "/etc/group" file, but it is convenient to use the vigr command to edit the "/etc/group" file. (The operation method is the same as vi)

The user's login history will be output to the /var/run/utmp and /var/log/wtmp files. This file, like the /var/log/lastlog and /var/log/btmp files, is a binary file, so it cannot be displayed by the less, cat, or tail commands. To display it, use the dedicated /usr/bin/last command.

To check which group a particular user belongs to, use the groups command. If you run the command with no arguments, the group to which the user who executed the command belongs will be displayed. If you specify the name of the user whose group you want to display as an argument, the group to which the user belongs will be displayed.

●Add a group To create a group, use the groupadd command. When executing this command, specify the group name to be added as an argument. You will need root privileges to run this command.

グループパスワードを削除する グループに設定したパスワードを削除するには、gpasswdコマンドにオプション「-r」か...

To set a password for a group, use the gpasswd command You will be prompted to enter a password when adding a user to a group or when a user is not registered in a group. By setting a password for the group, you can prevent people from registering members to the group without permission.

You can set up an administrator for an existing group separately from root (privileged user). The administrator set here can add and remove members, set and remove group passwords, etc. for the group. To set up an administrator, add the option "-A" to the gpasswd command and specify the user name and the group name to be managed as arguments. Multiple users can be specified by separating them with a comma ",".