Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 6 ■ SECURING YOUR SYSTEMSfrom="mydesktop.example.com",■ Note To limit it to allow this key to be used within your domain only, you can use wildcard pattern matching:from="*.example.com",However, note that, like any domain-based access control, this is vulnerable to an attack from someone setting upreverse DNS lookup that contains your domain.Copy the whole contents of tmpfile into /root/.ssh/authorized_keys2 on every machine you wantto be able to log into with this key.■ Note Make sure it’s a single line for each key!Check that the permissions on /root/.ssh/ on every machine are correct, because SSH is very pickyabout permissions:chmod -R go-rx /root/.sshchown -R root:root /root/.sshTest that this works as expected by running the following from your desktop machine:ssh root@test.example.com -i ~/.ssh/root_key■ Note See recipe 6-5 for how to set your SSH options so the key is picked up automatically.If all is well, you can edit your /etc/ssh/sshd_config files on all your machines to allow root loginonly with an SSH key:PermitRootLoginwithout-passwordThis doesn’t mean that you can log in without specifying a password! It means that you can’t use thepassword auth mechanism but have to use an SSH key.See recipe 6-3 for another example of limiting an SSH key—in that case, when using rsync andwanting to be able to use it passphrase-free.136Download at WoweBook.Com
CHAPTER 6 ■ SECURING YOUR SYSTEMS6-2. Managing Keys with KeychainAs discussed in the previous recipe, using SSH keys has many advantages, but one of the major onesshows up only if you use keychain to manage your keys. keychain is a small script that improves on sshagent.ssh-agent will cache your keys for you (so that you need to enter your passphrase only once perterminal session for each key), but by default, it won’t run across shell sessions. So, if you set it to start inyour ~/.bash_profile, you’ll still have to type your passphrase once per new terminal session.■ Note If you use GDM, ssh-agent will start by default on login. Otherwise, add this line to your ~/.xsessionfile:ssh-agent gnome-sessionsubstituting in whatever window manager you use for gnome-session. Now, to add a key, type ssh-add~/.ssh/key_name.keychain improves on ssh-agent by checking for a running ssh-agent process when you log in andeither hooking into one if it exists or starting a new one up if necessary. (Some X GUI environments alsohave something similar available.) To set up keychain, first install the keychain and ssh-askpasspackages for your system. For Debian/Ubuntu, use this:sudo apt-get install keychain ssh-askpassNow edit your ~/.bash_profile file to include these lines:01 #!/bin/bash02 /usr/bin/keychain ~/.ssh/id_rsa ~/.ssh/id_dsa > /dev/null03 source ~/.keychain/hostname-shIn line 02, you should include the paths to any keys that you want keychain to manage; check your~/.ssh directory. For example, if you’ve used recipe 6-1, you’ll have a ~/.ssh/root_key key, and line 02will read as follows:02 /usr/bin/keychain ~/.ssh/id_rsa ~/.ssh/id_dsa ~/.ssh/root_key > /dev/nullRoute the output to /dev/null to avoid getting the agent information output to the screen everytime you start a new terminal. Line 03 sources ~/.keyring/hostname-sh (which is created when keychainfirst runs to store ssh-agent information) to access SSH_AUTH_SOCK, which records the Unix socket thatwill be used to talk to ssh-agent. Obviously, you should replace hostname with the name of the hostyou’re using.The first time the keychain process is started up (so, the first time you log in after setting this up),you’ll be asked to enter the passphrases for any keys that you’ve listed on line 02. These will then bepassed into ssh-agent. Once you have a bash prompt, try logging into a suitable machine (that is, one137Download at WoweBook.Com
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Contents■About the Author .......
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■ CONTENTS3-7. Writing a Nagios P
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■ CONTENTS■Chapter 8: Using the
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■ CONTENTSAbout the Author■Juli
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■ CONTENTSAcknowledgmentsMany tha
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■ CONTENTSIntroductionThis book i
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■ INTRODUCTIONDownloading the Cod
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C H A P T E R 1■ ■ ■Saving Yo
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CHAPTER 1 ■ SAVING YOURSELF EFFOR
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C H A P T E R 2■ ■ ■Centraliz
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CHAPTER 2 ■ CENTRALIZING YOUR NET
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C H A P T E R 3■ ■ ■Monitorin
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CHAPTER 3 ■ MONITORING AND UPDATI
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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 BUGSAn
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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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