SA class 3

user management:
    uid / gid                  # user id / group id
    uid == 0                   # I am a root!
    deamon                     # unprivileged software
    bin                        # system comnands
    sys                        # kernel and memory images
    nobody                     # a Korean song (?


Add a user:
    edit password and group files:
        vipw                   # use vi to edit it
        pw

    set initial password:
        passwd usermane        # set password for an user
        passwd                 # for root

    set quota
        edquota usermane

    create user's home
        mkdir /home/username

    set some startup files
        cp some file like '.tcshrc' for the user

    set file/dir owner to the user
        chown -R username:group /home/user

    the command 'useradd' is your friend!



/etc/passwd                    # data separated by ':'
    login name
    passwd (Encrypted)
    uid
    default gid
    GECOS info
    Home directory
    Login shell


Encrypted password:
    /etc/master.passwd         # for BSD
    /etc/shadow                # for Linux

Encrypted method:
    DES
        8 char => 13 char
    md5
        arbitary length => 34 char starts with $1$
    blf
        arbitary length => 60 chr starts with $2$


GECOS:                         # data separated by ','
    General Electric Comprehensive Operation System
    finger username
    chfn to change it
    it is useless


Login shell
    /bin/{sh, csh, tcsh, bash, zsh}
    chsh to change it


/etc/group
    group name
    encrypted password
    GID
    list of members, separated by “,”
    only members in wheel group can do 'su' command


/etc/master.passwd             # for freeBSD
    vipw to edit
    additional fields
        login class
            /etc/login.conf
        passwd change time
        account expiration time


/etc/login.conf
    cap_mkdb /etc/login.conf   => login.cong.db


add user in Linux:
    /etc/passwd
        pwconf transfer to /etc/shadow
        Login name
        Encrypted Passwd
        Date of last password change
        ...

    init password
        passwd username

    set quota
        edquota username

    make home
        mkdir /home/username

    start files
        system wide:
            /etc/{csh.cshrc, csh.login, csh.logout, profile}
        private (home)
            .cshtc .tcshrc .login .logout
            .profile (sh)
            .vimrc   (vim)
            .xinitrc (startx)

    change owner
        chown -R username:group /home/username

Remove accounts
    delete user
        vipw, pw userdel             # BSD
        edit /etc/passwd and pwconv  # Linux

    backup home and mail
        tar /home/username and /var/mail/username
        chmod 600 the tar-ed files
    Delete home and mailbox
        rm -rf /home/username /var/mailusername

disable login
     change user's login shell as /sbin/nologin
     put a '#' or '-' in front of the account
     put a '*' in the encrypted password field

the root (God)
    root is God, i.e. you can do anything!
    uid == 0

    becoming root
        change your uid to 0
        sshd:
            edit /etc/ssh/ssh_config
            PermitRootLogin yes      # don't do it!
    su
        su username
        change to target user

    sudo
        a limited su
        visudo to edit sudoers
        edit /usr/local/etc/sudoers

===============================

chinese word

    ascii
        8 bits for 256 char
        0x00 ~ 0x1F : control characters
        0x20 ~ 0x7F : printable characters
    Big5
    unicode
        utf8, utf16

    chinese environment:
        訊息
        顯示
        輸入
        列印
        處理

    locale
        LC_ALL
        LC_CTYPE
        LC_MESSAGES
        LC_TIME
        LC_NUMERIC
        LC_MONETARY
        LC_COLLATE
        LANG

        power: LC_ALL > LC_* > LANG

    tcsh shell
        setenv LC_TYPE zh_TW.UTF-8
    bash
        export LC_CTYPE=zh_TW.UTF-8

    font type
        bitmapped font
        truetype font (ttf)


===============================

Controlling Processes:
    'program' to 'process'
        program is dead and lie on disk    # EX. /usr/bin/grep
        when you execute it, it becomes a process
        process is alive, it resides in memory
        process lives in
            an address space in memory
            kernel data structures

    attribute of the process
        PID PPID               # Process ID and its father's PID
        UID EUID               # User ID and Effective user ID
        GID EGUD               # Group ID amd Effective group ID
        Niceness               # priority of the process

        fork()
            == 0 child
             > 0 parent

    a life of process
        fork
            child has the same program context
        exec
            child use exec to change the program context
        exit
            child use _exit to tell kernel that it is ready to die and this
death
            should be acknowledged by the child’s parent
        wait
            parent use wait to wait for child’s death
            If parent died before child, this orphan process will have init as
it’s new parent

    UID, GID, EUID, EGID
        the effective uid and gid can be used to enable ir restric the
additional permissions

    Signal -- what happen to the process
        signal can be sent
            as a means of communication
            to kill, intertupt, or suspend process
                Ex. Ctrl-c, Ctrl-z, bg, fg  (background / frontground)

    you can catch, ignore block the SIG

    Kill a pid
        kill [-signal] pid
            kill -9
            kill -15

        killall name

    Niceness
        high nice value => low priority (好人卡)
        inherent property: 當你爸是好人，你也是好人
        only root can set nice value

    Process States
        I  Idle
        R  Runnable
        S  Slepping
        T  Stopped
        Z  Zombie
        D  in Disk

    ps command
        ps aux
        ps auxww
        ps -j
        ps -o
        ps -L

    top / htop

    Runaway process
        kill it!
            kill -15
            kill -9
        renice a higher nice value   # 發好人卡給他