向ubuntu系统中添加新的用户：username
sudo useradd -s /bin/bash -d /home/username/ -m username
sudo passwd username
以下是useradd命令的options，用到的选项已经标记为红色
Usage: useradd [options] LOGIN useradd -D useradd -D [options] Options: -b, --base-dir BASE_DIR base directory for the home directory of the new account -c, --comment COMMENT GECOS field of the new account -d, --home-dir HOME_DIR home directory of the new account -D, --defaults print or change default useradd configuration -e, --expiredate EXPIRE_DATE expiration date of the new account -f, --inactive INACTIVE password inactivity period of the new account -g, --gid GROUP name or ID of the primary group of the new account -G, --groups GROUPS list of supplementary groups of the new account -h, --help display this help message and exit -k, --skel SKEL_DIR use this alternative skeleton directory -K, --key KEY=VALUE override /etc/login.defs defaults -l, --no-log-init do not add the user to the lastlog and faillog databases -m, --create-home create the user's home directory -M, --no-create-home do not create the user's home directory -N, --no-user-group do not create a group with the same name as the user -o, --non-unique allow to create users with duplicate (non-unique) UID -p, --password PASSWORD encrypted password of the new account -r, --system create a system account -R, --root CHROOT_DIR directory to chroot into -s, --shell SHELL login shell of the new account -u, --uid UID user ID of the new account -U, --user-group create a group with the same name as the user -Z, --selinux-user SEUSER use a specific SEUSER for the SELinux user mapping --extrausers Use the extra users database