There are 3 type of user Super user /admin ---> root Normal user System user To Create new user (Normal) #adduser username #useradd username to change passwd for normal user #passwd username to change root password. #passwd /etc/passwd (File for user password and user name information) file with 7 field . 1 : 2 : 3 : 4 :5: 6 : 7 xyz : X : 501 : 501 : : /home/xyz :/bin/bash username:password:userid:groupid:finger information:home dir :shell whenever we create user /etc/defaults/useradd file has read by system /etc/defaults/useradd to give a special permission /etc/defalts/useradd group = 100 * disallow the user home = /home inactive = -1 Expire = !! disallow the user Shell = /bin/bash Skel = /etc/skel To clear Password. #vi /etc/passwd 2nd field of this file is :x: password information :x: does means user having password. If we remove :x: (x) password will be null (blank) --------------------------------------------------------------------- Password reset for Root User. If we have current password then simple process #passwd Enter new password : Conform new Password : If we haven’t password for Root: Stat system ----> Press E (edit Grub file’s line by edit it may ask grub password )put password and edit line Put single --------> in spite of : RO Press b (For boot) System start with Single user: It will prompt # Put command #passwd (And change password). If we haven’t password for Grub: Start your system----------> with 1st disk of installed os. (it could be Centos,redhat ,any Linux flavors which is installed) After booting from CD linux installation prompt will come :linux rescue ( type this to rescue password) mount file system: hit command # passwd Password Group and user related Configuration files. /etc/passwd /etc/gshadow /etc/login.defs /etc/group /etc/skel /etc/defaults/useradd /etc/shadow /etc/shells #useradd username #useradd –u 555 username (to give special UID) # useradd –s /bin/sh username (to assign special Shell) # useradd –e 2007-7-29 username (Assigning Expiry date) # useradd –f 10 username (de active after certain day) # useradd –G group1,group2,group3 username (add in multi group) #mkdir ghar #useradd –d /ghar/newusername newusername (to assign particular home directory for user) # useradd –d badman username (not tested above command please verify command by testing) # useradd –l newuser exiting username (to change login name) # useradd –c “user is for testing” username (to add comment on user) to Edit exiting User use all above commands with #usermod (page no 11,12 commands) #usermod –L username (to lock user) #usermod –U username (to unlock user) #chsh username (to change shell) #chfn username (to change finger information) #finger username (display finger information of user) #useradd –u 707 –c “all field” –e 2007.10-29 –s /bin/sh –G g1,g2,g3 (add user name with particular uid (707),comment ,time ,shell and multi group) # Add root user #useradd –u 0 –o –g 0 username (To add root user 0 (zero) is uid for root) #who am I (to know which user login) SUDO User # /etc/sudoers To make other user to limited administrator or full administrator. #visudo To give command in sudo user #sudo command path #visudo (we can add sudo user in this file , also can add wheel (root) group and edit user. #allow b1 ALL=(ALL) ALL # % wheel ALL Adding Alias for SUDO #user_alias U=nl Cmmd_Alias C= /usr/sbin/useradd , more commands if required #common Alias cmnd_Aliasc=/usr/sbin/useradd U ALL = C Also can Add more alias like “Network” U ALL = NETWORKING #useradd –G groupname User_Alias U = n1 Cmnd_alias C= /usr/sbin/useradd U ALL = C Group To Create group and assign different login IDs #vi /etc/login.defs #id –u username (to know about particular user ID) #groupadd newgroupname /etc/group #useradd –G groupname newusername #groupdel groupname #usermod –G groupname existing username /etc/shadows to know password information (Linux use MD5 protection for encryption ) /etc/shadows has 8 field . fields username : username (root) encryption :$d7748jj%&^fb (add ! before $ to inactive user) days remaining : Remaining days before expire change password :(after how many day user has to change passwd) password must change :(after how many day passwd must change) warning : password expiry warning inactive :user will inactive after days days counting : since user created /etc/skel Whatever file stored in this folder are automatically added for new user creation. #vi /etc/group Groupname:password:groupid /etc/gshadows to know about group password groupname: password: users #gpasswd (to change group password) #groupadd group name #groupadd –u gid (group add with special gid. means particular gid no {I.E 1000} ) #groupdel groupname #grupmod (with all about switch for exiting group) |
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