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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Login ShellEnvironmentSecurity IssuesSummary

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

L ogin Shell

Linuxs interactive command interpreter.Provide a layer around the system functions,invokecommandsThe mean interactive users access to many utilitiesShell not a part of the operating system kernelLinux provide three standard shells

Bourne again shell (bash)tcshksh

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Environment

Two file executed when login:The system-wide initialization file /etc/profileThe personal initialization file ~/.bash_profile or

~/.bash_login or ~/.profile.Contain system commandsProvide a common environment for all users

Set a user-customized environmentContain user commands and definitions

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Environment

Interactive non-login shells:Bash look for the environments ~/.bashrc andexecute it.Execute file was assigned by BASH_ENVExecute file was assigned by ENVExecute /etc/bashrc file

/etc/profile and /etc/bashrc files contain system-widecommands.$HOME/.bash_profile,.bash_login,.profile,.bashrc,.bash_logout contain users initialization

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Environment

Environment Definition: user modify some of theenvironmental definitions to suite their requirements.PATH=$PATH:/usr/X11R6/binBASH_ENV=$HOME/.bashrc

SHELL=/bin/bashPS1=[\u@\h\w]\$VISUAL=viMAIL=/var/spool/mail/$LOGNAME

The umask commandumask plain text file (vi)000 rw-rw-rw-022 rw-rr

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Security Issues

Under traditional UNIX message of the day (motd)store in /etc/motd. Login program printed themessage of the day affter a successful login and

before executing users login shell.Under linux motd be configurable through PAM(pluggable authentication modules) by addingapropriate references to pam_motd.so in /etc/pam.d

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Security Issues

Guest account with null password be a security risk,usually set disableSystem hacker logging as guest can:

Get list of login name (/etc/passwd)Use find to look for security holesFind out about networked machines (/etc/hosts)Access the network via telnet or rlogin

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Security Issues

SGID2xxx

SUID

4xxxSTICKY BIT

1xxx

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SAIGONLAB83 Nguy n Th Nh , P9, Q.Tn B nh, Tp. HCM LPI 102

Summary

Contrust different login profiles and user accountsDefine, explain, and modify user environmentsExplain security issues