Linux System Administration Recipes A Problem-Solution Approach

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CHAPTER 6 ■ SECURING YOUR SYSTEMSHost desktop.example.comForwardX11Trusted yesHost *ForwardX11 yesSince ssh picks up the first option it encounters, for desktop.example.com that first setting will beused, while all other hosts will fall through to the second setting.6-6. Transferring Files Over an Existing ssh Connectionssh is an excellent and essential tool, but it does have one major lack: the inability to transfer files withina session. Of course, you can use scp for this job, but it’s a nuisance to have to fire up anotherconnection for the transfer when you’re already connected to that machine!A possible solution is ssh-xfer, which uses the local SSH agent to transfer files using an existingconnection. It can also do this over multiple connections, which means that if you’ve ssh’d into desktopA and then through that to server B, ssh-xfer will allow you to transfer a file directly from server B toyour local machine.■ Note ssh-xfer is limited in that, at least currently, you can transfer files only from the remote machine to thelocal machine, not vice versa.Unfortunately, currently ssh-xfer isn’t a standard part of the ssh setup, so you’ll need to patch yourssh-agent locally and install the ssh-xfer binary remotely. However, you can put the binary in your owndirectory on the remote server, so you don’t need root access to that machine.To get this set up, you’ll need the OpenSSH source code locally so you can apply the patch and buildthe ssh-xfer binary. Download the OpenSSH patch from the ssh-xfer web site at http://matt.ucc.asn.au/ssh-xfer/, and save it to the OpenSSH source directory. Then run the followingpatch -p0 < patch-file-nameNext, build the ssh-xfer binary, in the same directory, with this:./configure; make ssh-xferFinally, you must transfer the ssh-xfer binary to the remote server:scp ssh-xfer myuser@remote.server.example.com:bin/ssh-xferNow, run a bash shell via the new agent on your local machine:ssh-agent-xfer bash142Download at WoweBook.Com
CHAPTER 6 ■ SECURING YOUR SYSTEMSThis will open a new shell, running with the patched ssh-agent. Then open a connection to theremote server with agent forwarding enabled (the -A option):ssh -A myuser@remote.server.example.com■ Note If you’re going to do this regularly, see recipe 6-5 for advice on how to set your ssh options in~/.ssh/config so the -A option is automatically set for this machine.From this shell on the remote server, type this:~/bin/ssh-xfer testfile.txttestfile.txt will be put in ~/Desktop on your local machine. You can change this default locationby editing the XFER_DEST_DIR value in the ssh-xfer patch, before you do the patching.■ Note Enabling agent forwarding is a slight security risk, but the convenience may well be worth it! You can alsochoose to use the patched binary only when you know you’re likely to be transferring files and similarly only to useagent forwarding in those circumstances.6-7. Kerberizing Your SSH SetupIf you Kerberize your SSH setup, you can log on to other machines in your network using your existingKerberos ticket (that is, without entering your password), which saves time and keystrokes (alwaysimportant for sysadmins!).The current version of SSH in Debian/Ubuntu has Kerberos authentication support built in, but youhave to edit /etc/ssh/sshd_config on the server to allow it to be used. Make sure you have these lines inthat file:# Kerberos optionsKerberosAuthentication yesKerberosOrLocalPasswd yes# GSSAPI optionsGSSAPIAuthentication yes143Download 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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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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Linux System Administration Recipes A Problem-Solution Approach

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