TAILIEUCHUNG - Module Linux essentials - Module 13: System and user security

Module Linux essentials - Module 13 introduce basic security and identifying user types. After studying this chapter students should be able to: Working with root and standard users, understanding system users. | Module 13 System and User Security Exam Objective Basic Security and Identifying User Types Objective Summary Working with Root and Standard Users System Users User accounts and passwords User accounts Files in the /etc directory contain account data. The /etc/passwd file defines some of the account information for user accounts. The /etc/passwd file Each line of the /etc/passwd file relates to a user account. Each line is separated into fields by colon characters. The fields from left to right are as follows: name:password placeholder:user id:primary group id:comment:home directory:shell The /etc/passwd file Field Example Description name root This is the name of the account. password placeholder x The x in the password placeholder field indicates to the system that the password is not stored here, but rather in the /etc/shadow file. user id 0 Each account is assigned a user ID (UID). primary group id 0 When a user creates a file, the file is owned by a group id (GID), the user's primary GID. comment root This field can contain any information about the user, including their real (full) name and other useful information home directory /root This field defines the location of the user's home directory. shell /bin/bash This is the location of the user's login shell. The /etc/shadow file Contains account information related to the user's password. The fields of the /etc/shadow file are: name:password:lastchange:min:max:warn:inactive:expire:reserved The /etc/shadow file Field Example Description name sysadmin This is the name of the account, which matches the account name in the /etc/passwd file. password $6$.rl1 The password field contains the encrypted password for the account. last change 15020 This field contains a number that represents the last time the password was changed. min 5 The password can't be changed again for the specified number of days. max 30 This field is used to force users to change their passwords on a regular basis warn 7 If the

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