add user, group, show list all user or group on Centos 6

On Centos 6, you may freely create user, group. Now I give some example for these.

1. Create a group hadoop (it will be saved into /etc/group )

Usage: groupadd [options] GROUP

Options:
  -f, --force                   exit successfully if the group already exists,
                                and cancel -g if the GID is already used
  -g, --gid GID                 use GID for the new group
  -h, --help                    display this help message and exit
  -K, --key KEY=VALUE           override /etc/login.defs defaults
  -o, --non-unique              allow to create groups with duplicate
                                (non-unique) GID
  -p, --password PASSWORD       use this encrypted password for the new group
  -r, --system                  create a system account

e.g.
 sudo groupadd hadoop

2.  Create one user hduser (it will be save into /etc/passwd)

sage: useradd [options] LOGIN

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
  -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

e.g.
useradd -g hadoop hduser

3. show list all users
cat /etc/passwd | cut -d ":" -f 1

4: show list all groups


cat /etc/group |cut -d ":" -f 1



For cat and cut, please refer the following help

5. cat


Usage: cat [OPTION]... [FILE]...
Concatenate FILE(s), or standard input, to standard output.

  -A, --show-all           equivalent to -vET
  -b, --number-nonblank    number nonempty output lines
  -e                       equivalent to -vE
  -E, --show-ends          display $ at end of each line
  -n, --number             number all output lines
  -s, --squeeze-blank      suppress repeated empty output lines
  -t                       equivalent to -vT
  -T, --show-tabs          display TAB characters as ^I
  -u                       (ignored)
  -v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB
      --help     display this help and exit
      --version  output version information and exit

With no FILE, or when FILE is -, read standard input.

Examples:
  cat f - g  Output f's contents, then standard input, then g's contents.
  cat        Copy standard input to standard output.

6. cut

Usage: cut OPTION... [FILE]...

Print selected parts of lines from each FILE to standard output.

Mandatory arguments to long options are mandatory for short options too.

  -b, --bytes=LIST        select only these bytes

  -c, --characters=LIST   select only these characters

  -d, --delimiter=DELIM   use DELIM instead of TAB for field delimiter

  -f, --fields=LIST       select only these fields;  also print any line

                            that contains no delimiter character, unless

                            the -s option is specified

  -n                      with -b: don't split multibyte characters

      --complement        complement the set of selected bytes, characters

                            or fields

  -s, --only-delimited    do not print lines not containing delimiters

      --output-delimiter=STRING  use STRING as the output delimiter

                            the default is to use the input delimiter

      --help     display this help and exit

      --version  output version information and exit

Use one, and only one of -b, -c or -f.  Each LIST is made up of one

range, or many ranges separated by commas.  Selected input is written

in the same order that it is read, and is written exactly once.

Each range is one of:

  N     N'th byte, character or field, counted from 1

  N-    from N'th byte, character or field, to end of line

  N-M   from N'th to M'th (included) byte, character or field

  -M    from first to M'th (included) byte, character or field

With no FILE, or when FILE is -, read standard input.