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Chapter 7 Administering the system CompTIA Linux+ (3.Using system log…

- - - - usermod
        
        Changes an existing account instead of creating a new one
      - change
        
        To modify account settings relating to account expiration
      - Setting a password
        
        passwd [-k] [-l] [-u -f]] [-d] [-S] [username]
      - Directly modifying account configuration files
        
        User configuration files can be modified directly. The /etc/passwd and /etc/shadow files control most aspects of an account's basic features.
      - Adding users
        
        useradd [-c comment] [-d home-dir] [-e expire-date] [-f inactive-days] [-g default-group] [-G group[,...]] [-m [-k skeleton-dir] | -M] [-p password] [-s shell] [-u UID [-o]] [-r] [-n] username
      - userdel
        
        Used to delete user's entries from /etc/passwd and /etc/shadow
  - - - groupmod [-g GID [-o]] [-n newgroupname] oldgroupname
    - - groupmod [-g GID [-o]] [-n newgroupname] oldgroupname
    - - groupadd [-g GID [-o]] [-r] [-f] groupname
- - - - You may think that locating an NTP server with a low stratum number (such as stratum 1) is ideal. Although it’s true that your own system will have a minutely more accurate clock when using such a source, the best approach in most cases is to synchronize with a stratum 2 or lower system.
    - - When you’re setting up a network to use NTP, select one system (or perhaps two for a network with several dozen or more computers) to function as the primary NTP server. This computer needn’t be very powerful, but it must have always-up access to the network. You can then install the NTP server and configure it.
    - - NTP enables an expanding pyramid of computers to set their clocks to a highly accurate source signal.
- - - - Sometimes cron and anacron are overkill. You may simply want to run a single command at a specifi c point in the future on a one-time basis rather than on an ongoing basis. For this task, Linux provides another command: at.
    - - This program is designed as a supplement to cron to ensure that regular maintenance jobs are executed at reasonable intervals. It works by keeping a record of programs it should execute and how frequently it should do so, in days. Whenever anacron is run, it checks to see when it last executed each of the programs it’s configured to manage.
    - - The cron program is a daemon, so it runs continuously, looking for events that cause it to spring into action. Unlike most daemons, which are network servers, cron responds to temporal events. Specifically, it “wakes up” once a minute, examines configuration files in the /var/spool/cron and /etc/cron.d directories and the /etc/crontab file, and executes commands specified by these configuration files if the time matches the time listed in the files.
      - Creating System cron Jobs
        
        The /etc/crontab file controls system cron jobs. This file normally begins with several lines that set environment variables, such as $PATH and $MAILTO (the former sets the path, and the latter is the address to which programs’ output is mailed). The file then contains several lines that resemble the following: 02 4 * root run-parts /etc/cron.daily
      - Creating User cron Jobs
        
        crontab [-u user] [-l | -e | -r] [file]