Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 2 ■ CENTRALIZING YOUR NETWORK: KERBEROS, LDAP, AND NFSYou should be challenged for the admin user’s password after the first command. Then the secondwill show you a list of authorized tickets, and you’ll see that you have an authorized principal krbadm inthere.2-1b. Kerberos Client SetupFor Debian/Ubuntu, use this:sudo apt-get install krb5-user ntpdatekrb5-user provides the klist and kinit utilities. ntpdate is needed because the time on the serverand client must match for the authentication to succeed (so that an attacker can’t use an out-of-daterequest).Edit /etc/krb5.conf to make sure that the following entries are correctly set—it should match yourserver setup values:[libdefaults]default_realm = EXAMPLE.COM[realms]EXAMPLE.COM = {kdc = kerberos.example.comadmin_server = kerberos.example.com}[domain_realm]example.com = EXAMPLE.COM.example.com = EXAMPLE.COM2-2. Setting Up Kerberos SSH and LogonThis recipe explains how to set up both the server and clients to use Kerberos for console or gdm logonand for SSH logon. Server here refers to any machine that you’re using ssh to connect to, and client refersto any machine that you’re using ssh from. We’ll use PAM to handle both ssh and local login. ForDebian/Ubuntu, run this:sudo apt-get install libpam-krb5 openssh-server libsasl2-dev libsasl2-modules-gssapi-mitEdit /etc/pam.d/common-auth and /etc/pam.d/common-session to use pam_krb5.so.1 (replace any existing lines):# /etc/pam.d/common-authauth sufficient pam_krb5.so use_first_pass ignore_root forwardableauth required pam_unix.so nullok_secure try_first_pass# /etc/pam.d/common-sessionsession sufficient pam_unix.sosession sufficient pam_krb5.so ignore_root26Download at WoweBook.Com
CHAPTER 2 ■ CENTRALIZING YOUR NETWORK: KERBEROS, LDAP, AND NFSThe sufficient line enables local login (for example, by root) if necessary (for example, if there arenetwork problems). At least one line in common-auth must be required, or you will be able to log inwithout a password!The use_first_pass and try_first_pass options mean that you get asked for your password onlyonce, whichever module is used—the second module to attempt authentication will use the alreadyentered password. ignore_root means that the Kerberos module is not used for root login and improvessecurity.To set up ssh login, edit /etc/ssh/sshd_config to set the various Kerberos options (edit these lines ifalready present; add them if not):KerberosAuthentication yesKerberosOrLocalPasswd yesKerberosTicketCleanup yesUsePAM yesAllowTcpForwarding yesGSSAPIAuthentication yesGSSAPICleanupCredentials yesGssapiKeyExchange yesThen edit /etc/ssh/ssh_config (not sshd_config!) to set these lines:GSSAPIAuthentication yesGSSAPIDelegateCredentials yesMake these edits on both the server and the client side. (In practice, therefore, just make the editsfor every machine in your network that you use ssh to or from.) Then restart the ssh server (on allmachines you’ve edited) with sudo /etc/init.d/sshd restart after you’ve made the configurationchanges.You need to add the client host to the keytab on the client so that ssh can transfer the Kerberoscredentials. From the client, run kadmin -p krbadm, which authenticates you to the admin server as theadmin user and connects you to the admin server. Then execute these commands:kadmin: addprinc -randkey host/client.example.comkadmin: ktadd host/client.example.comThe -randkey option generates a random key rather than asking for a password, and this ispreferable for a nonperson entity like a machine, meaning that the key is stored locally and used todecrypt a granted TGT, rather than a password having to be entered. The ktadd line adds the server keyto the local default keyfile (/etc/krb5.keytab).Create a test user, still using kadmin:kadmin: addprinc test@EXAMPLE.COM27Download at WoweBook.Com
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Page 7 and 8: Contents■About the Author .......
Page 9 and 10: ■ CONTENTS3-7. Writing a Nagios P
Page 11 and 12: ■ CONTENTS■Chapter 8: Using the
Page 13 and 14: ■ CONTENTSAbout the Author■Juli
Page 15 and 16: ■ CONTENTSAcknowledgmentsMany tha
Page 17 and 18: ■ CONTENTSIntroductionThis book i
Page 19 and 20: ■ INTRODUCTIONDownloading the Cod
Page 21 and 22: C H A P T E R 1■ ■ ■Saving Yo
Page 23 and 24: CHAPTER 1 ■ SAVING YOURSELF EFFOR
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C H A P T E R 4■ ■ ■Taking Ba
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CHAPTER 4 ■ TAKING BACKUPS AND MA
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C H A P T E R 5■ ■ ■Working w
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CHAPTER 5 ■ WORKING WITH FILESYST
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C H A P T E R 6■ ■ ■Securing
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CHAPTER 6 ■ SECURING YOUR SYSTEMS
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CHAPTER 7 ■ WORKING WITH APACHEOn
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CHAPTER 7 ■ WORKING WITH APACHEAl
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C H A P T E R 8■ ■ ■Making Be
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CHAPTER 8 ■ USING THE COMMAND LIN
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CHAPTER 9 ■ WORKING WITH TEXT IN
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C H A P T E R 10■ ■ ■Things G
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CHAPTER 10 ■ THINGS GO IN, THINGS
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C H A P T E R 11■ ■ ■Tracking
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CHAPTER 11 ■ TRACKING DOWN BUGSTh
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CHAPTER 11 ■ TRACKING DOWN BUGS01
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CHAPTER 11 ■ TRACKING DOWN BUGS
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CHAPTER 11 ■ TRACKING DOWN BUGSTh
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CHAPTER 11 ■ TRACKING DOWN BUGS#
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C H A P T E R 12■ ■ ■Managing
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CHAPTER 12 ■ MANAGING TIME AND PE
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APPENDIX■ ■ ■Perl TipsSee rec
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APPENDIX ■ PERL TIPS• Date::Par
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APPENDIX ■ PERL TIPSPerl Syntax N
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■ ■ ■Index■Symbols$CDPATH,
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■ INDEXenscript option (printing)
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■ INDEX■NNagiosadding hosts to,
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■ INDEXsyslogcentralized logging
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