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User account information files
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/ Etc / passwd: records all accounts on linux
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/ Etc / shadow: the record corresponding to the account password
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/ Etc / group: records all groups
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passwd structure:
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username
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Early versions of the user password, now the "X"
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UID: 0 indicates that the system administrator, 1-999 reserved for system
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GID: ditto
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Information of the user instructions
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The user's home directory, where the login directory
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Whether the user can use the shell
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shadow structure
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username
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Encrypted password
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Recently changed the password of the date, number of days counted from January 1, 1970
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The number of days the password can not be changed, 0 can be modified immediately
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The number of days you want to change your password, you can force users to change passwords by this method
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Password Change Warning Days
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Time after password expires, the account can also be used
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Account expiration time, the number of days counted from January 1, 1970
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Reserved position
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group structure:
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group name
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Group password (generally not required)
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GUIDE
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Affiliated group
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User-created
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useradd [username]: Create a user
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-u: Set UID
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-g: Set Primary Group
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-G: Setting affiliated group
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-c: set user Description
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-d: Specifies the user's home directory
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-s: Specifies the user shell
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-e: account expiration date in the format YYYY-MM-DD
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-f: Specifies the password is valid immediately failure 0, 1 and never fail
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User cryptographic operations
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passwd [username]: Change Password
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-l: lock the account
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-u: Unlock
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-s: display parameters account password
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-n: number of days to set how long you can not change your password
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-x: the number of days to set how often passwords must be changed within
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-w: the number of days, set a password expiration warning days
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-i: the number of days, number of days to set a password failure
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chage: Modify and password associated time parameters
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-l: View parameters
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-d: YYYY-MM-DD modified recently changed the password of a time
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-E: Modify the account expiration time
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-I: A few days after the failed password
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-m: Password retained for at least a few days
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-M: A few days after the password needs to be updated
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-w: Set password expiration warning time
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Delete user operation
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userdel [username]: delete users, does not remove the user's home directory and mailbox
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-r: delete the home directory and mailbox
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