Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 2 ■ CENTRALIZING YOUR NETWORK: KERBEROS, LDAP, AND NFSdn: ou=people,dc=example,dc=comobjectclass: organizationalUnitou: peopledescription: Usersdn: uid=ldapadm,ou=people,dc=example,dc=comobjectClass: inetOrgPersonobjectClass: posixAccountobjectClass: shadowAccountcn: LDAP admin accountuid: ldapadmuidNumber: 1002gidNumber: 100homeDirectory: /etc/ldaploginShell: /bin/false■ Note The LDAP user cannot log in directly, because the login shell is set to /bin/false. This is a securitymeasure. Alternatively, you could make objectClass be simpleSecurityObject instead of posixAccount.To add this file, use ldapadd:ldapadd -x -D "cn=admin,dc=example,dc=com" -W -f setup.ldif-W is the flag that causes the password to be demanded; -x uses an anonymous bind, because you’renot set up yet to use Kerberos. -ZZ would invoke TLS, which works on all the LDAP admin commands(ldapadd, ldapsearch, and so on).After this, edit /etc/ldap/slapd.conf again to remove (or comment out) the rootdn and rootpwentries. From now on, to add, delete, or modify entries, you can authenticate via Kerberos using kinitldapadm.Restart slapd with /etc/init.d/slapd restart.Testing!Before you fully populate the database, check that it works! Try the following, first from the server. Oncethat’s working, set up a client and try it from there.• ldapsearch -x -H ldaps://server.example.com (-x gives simple bind)• ldapsearch -x -H ldap://server.example.com -ZZ (to test TLS startup)• ldapsearch -x -H ldaps://server.example.com -ZZ -TLS• kinit username; ldapsearch -H ldaps://server.example.com (to testKerberos auth)34Download at WoweBook.Com
CHAPTER 2 ■ CENTRALIZING YOUR NETWORK: KERBEROS, LDAP, AND NFSTroubleshootingHere are some things to look for if it doesn’t work:• Check the permissions on /etc/ldap/cacert.pem. They need to be world-readable.• Check /etc/hosts if the hostname is resolving incorrectly. This will show up in thedebugging output. Your client must be trying server.example.com, not just server,because it must match what’s in the certificate.• If you get the error “Key version for principal in keytable is incorrect,” there is amismatch between the Kerberos keytab and the master server. On the LDAP host,run kadmin -p krbadm, and execute the following:ktrem ldap/server.example.comdelprinc ldap/server.example.comaddprinc -randkey ldap/server.example.comktadd ldap/server.example.com• If you get the error “GSSAPI Error: Miscellaneous failure (Permission denied),”check that the LDAP keytab is readable by the LDAP user (openldap) and that slapdis looking at the correct keytab. You can test this quickly by also addingldap/server.example.com to the system keytab at /etc/krb5.keytab and makingthat world-readable:kadmin -p krbadm -q "ktadd -k /etc/krb5.keytab ldap/server.example.com"chmod a+r /etc/krb5.keytabIf that starts things working, then your keytab may be the problem. Remember tochange /etc/krb5.keytab back to root-only afterward:chmod go-r /etc/krb5.keytaband remove the ldap/server.example.com entry from your main keytab:kadmin -p krbadm -q “ktrem -k /etc/krb5.keytab ldap/server.example.com”• Add -d 16383 to the ldapsearch line to enable copious debugging output.However, having high levels of debugging will slow things down hugely. That’sfine when setting up but not good for a production server. Turn debugging off ordown (set loglevel in /etc/ldap/slapd.conf to 0 or 1) once things are working. Ifyou are not getting errors but ldapsearch appears to be hanging, try reducing thelog levels in /etc/ldap/slapd.conf and restarting slapd.2-5. Populating the LDAP DatabaseThere are many options to populate the database. If you already have users, you’ll want to migrate yourdata. Use the migrationtools package on Debian. This works fine for regular Unix setup (/etc/passwd,/etc/shadow, /etc/groups) and also for NIS. With some adjustment, it will also work for NIS+. You’ll needto take a look at your NIS+ files and the migrationtools scripts and edit them as necessary. You will,however, need to migrate your passwords to Kerberos by hand. This may be a good moment to makeeveryone change their passwords!35Download 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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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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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 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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