7. Troubleshooting - Linux Games & Server
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1. versions 1 3 and 4 There are also different service listings depending on whether NFS is travelling over TCP or UDP UDP is usually but not always the default unless TCP is explicitly requested If you do not see at least portmapper nfs and mounta then you need to restart NFS If you are not able to restart successfully proceed to Symptom 9 Now check to make sure you can see it from the client On the client type rpcinfo p server where server is the DNS name or IP address of your server 04 12 2006 19 25 Troubleshooting http www tldp org HOWTO NFS HOWTO stroubleshooting html 3 von 6 If you get a listing then make sure that the type of mount you are trying to perform is supported For example if you are trying to mount using Version 3 NFS make sure Version 3 is listed if you are trying to mount using NFS over TCP make sure that is registered Some non Linux clients default to TCP Type man rpcinfo for more details on how to read the output If the type of mount you are trying to perform is not listed try a different type of mount If you get the error No Remote Programs Registered then you need to check your etc hosts allow and etc hosts deny files on the server and make sure your client actually is allowed access Again if the entries appear correct check etc hosts or your DNS server and make sure that the machine is listed correctly and make sure you can ping the server from the client Also check the error2. Troubleshooting http www tldp org HOWTO NFS HOWTO troubleshooting html 1 von 6 Linux NFS HOWTO Prev Next 7 Troubleshooting This is intended as a step by step guide to what to do when things go wrong using NFS Usually trouble first rears its head on the client end so this diagnostic will begin there 7 1 Unable to See Files on a Mounted File System First check to see if the file system is actually mounted There are several ways of doing this The most reliable way is to look at the file proc mounts which will list all mounted filesystems and give details about them If this doesn t work for example if you don t have the proc filesystem compiled into your kernel you can type mount f although you get less information If the file system appears to be mounted then you may have mounted another file system on top of it in which case you should unmount and remount both volumes or you may have exported the file system on the server before you mounted it there in which case NFS is exporting the underlying mount point if so then you need to restart NFS on the server If the file system is not mounted then attempt to mount it If this does not work see Symptom 3 7 2 File requests hang or timeout waiting for access to the file This usually means that the client is unable to communicate with the server See Symptom 3 letter b 7 3 Unable to mount a file system There are two common errors that mount produces when
3. You may need to reinstall your binaries if none of these ideas helps 7 10 File Corruption When Using Multiple Clients If a file has been modified within one second of its previous modification and left the same size it will continue to generate the same inode number Because of this constant reads and writes to a file by multiple clients may cause file corruption Fixing this bug requires changes deep within the filesystem layer and therefore it is a 2 5 item Prev Home Next Security and NFS Using Linux NFS with Other OSes 04 12 2006 19 25
4. cted a lot of timeouts perhaps due to network congestion perhaps due to an overloaded server and is throttling back the number of concurrent outstanding requests in an attempt to lighten the load The cause of these messages is basically sluggish performance See Section 5 for details c After mounting the following message appears on the client nfs warning mount version older than kernel 04 12 2006 19 25 Troubleshooting http www tldp org HOWTO NFS HOWTO troubleshooting html It means what it says You should upgrade your mount package and or am utils If for some reason upgrading is a problem you may be able to get away with just recompiling them so that the newer kernel features are recognized at compile time d Errors in startup shutdown log for lockd You may see a message of the following kind in your boot log nfslock rpc lockd startup failed They are harmless Older versions of rpc lockd needed to be started up manually but newer versions are started automatically by nfsd Many of the default startup scripts still try to start up lockd by hand in case it is necessary You can alter your startup scripts if you want the messages to go away e The following message appears in the logs kmem_create forcing size word alignment nfs _fh This results from the file handle being 16 bits instead of a mulitple of 32 bits which makes the kernel grimace It is harmless 7 7 Real permissions don t
5. erver that determines which uid root gets mapped to By default the server uses the UID and GID of nobody in the etc passwd file but this can also be overridden with the anonuid and anongia options in the etc exports file Make sure that the client and the server agree about which UID nobody gets mapped to 7 5 When I transfer really big files NFS takes over all the CPU cycles on the server and it screeches to a halt This is a problem with the fsync function in 2 2 kernels that causes all sync to disk requests to be cumulative resulting in a write time that is quadratic in the file size If you can upgrading to a 2 4 kernel should solve the problem Also exporting with the no_wdelay option forces the program to use o_sync instead which may prove faster 7 6 Strange error or log messages a Messages of the following format Jan 7 09 15 29 server kernel fh_verify mail guest permission failure acc 4 error 13 Jan 7 09 23 51 server kernel fh_verify ekonomi test permission failure acc 4 error 13 These happen when a NFS setattr operation is attempted on a file you don t have write access to The messages are harmless b The following messages frequently appear in the logs kernel nfs server server domain name not responding still trying kernel nfs task 10754 can t get a request slot kernel nfs server server domain name OK The can t get a request slot message means that the client side RPC code has dete
6. it is unable to mount a volume These are a failed reason given by server Permission denied This means that the server does not recognize that you have access to the volume i Check your etc exports file and make sure that the volume is exported and that your client has the right kind of access to it For example if a client only has read access then you have to mount the volume with the ro option rather than the rw option ii Make sure that you have told NFS to register any changes you made to etc exports since starting nfsd by running the exportfs command Be sure to type exportfs ra to be extra certain that the exports are being re read iii Check the file proc fs nfs exports and make sure the volume and client are listed correctly You can also look at the file var 1ib nfs xtab for an unabridged list of how all the active export options are set If they are not then you have not re exported properly If 04 12 2006 19 25 Troubleshooting 2 von 6 iv http www tldp org HOWTO NFS HOWToO troubleshooting html they are listed make sure the server recognizes your client as being the machine you think it is For example you may have an old listing for the client in etc hosts that is throwing off the server or you may not have listed the client s complete address and it may be resolving to a machine in a different domain One trick is login to the server from the client via ssh or telnet if you then type who one of the
7. listings should be your login session and the name of your client machine as the server sees it Try using this machine name in your etc exports entry Finally try to ping the client from the server and try to ping the server from the client If this doesn t work or if there is packet loss you may have lower level network problems It is not possible to export both a directory and its child for example both usr and usr local You should export the parent directory with the necessary permissions and all of its subdirectories can then be mounted with those same permissions b RPC Program Not Registered or another RPC error This means that the client does not detect NFS running on the server This could be for several reasons i ii First check that NFS actually is running on the server by typing rpcinfo p on the server You should see something like this program vers proto 100000 2 tcp portmapper 100000 udp portmapper 100011 udp rquotad 100011 udp rquotad 100005 udp mountd 100005 tcp mountd 100005 udp mountd 100005 tcp mountd 100005 udp mountd 100005 tcp mountd 100003 udp nfs 100003 nfs 300019 1 amd 300019 1 amd 100024 1 status 100024 1 status 100021 1 nlockmgr 100021 nlockmgr 100021 nlockmgr 100021 1 nlockmgr 100021 nlockmgr 100021 nlockmgr WNHNHWWNHNFPRFNEF NY This says that we have NFS versions 2 and 3 rpc statd version 1 network lock manager the service name for rpc lockd
8. logs on the system for helpful messages Authentication errors from bad etc hosts allow entries will usually appear in var log messages but may appear somewhere else depending on how your system logs are set up The man pages for syslog can help you figure out how your logs are set up Finally some older operating systems may behave badly when routes between the two machines are asymmetric Try typing tracepath server from the client and see if the word asymmetric shows up anywhere in the output If it does then this may be causing packet loss However asymmetric routes are not usually a problem on recent linux distributions If you get the error Remote system error No route to host but you can ping the server correctly then you are the victim of an overzealous firewall Check any firewalls that may be set up either on the server or on any routers in between the client and the server Look at the man pages for ipchains netfilter and ipfwadm as well as the PChains HOWTO and the Firewall HOWTO for help 7 4 I do not have permission to access files on the mounted volume This could be one of two problems If it is a write permission problem check the export options on the server by looking at proc fs nfs exports and make sure the filesystem is not exported read only If it is you will need to re export it read write don t forget to run exportfs ra after editing etc exports Also check proc mounts and make sure the volume is
9. match what s in etc exports etc exports is very sensitive to whitespace so the following statements are not the same export dir hostname rw no_root_squash export dir hostname rw no_root_squash The first will grant hostname rw access to export dir without squashing root privileges The second will grant hostname rw privileges with root squash and it will grant everyone else read write access without squashing root privileges Nice huh 7 8 Flaky and unreliable behavior Simple commands such as Is work but anything that transfers a large amount of information causes the mount point to lock This could be one of two problems i It will happen if you have ipchains on at the server and or the client and you are not allowing fragmented packets through the chains Allow fragments from the remote host and you ll be able to function again See Section 6 4 for details on how to do this ii You may be using a larger rsize and wsize in your mount options than the server supports Try reducing rsize and wsize to 1024 and seeing if the problem goes away If it does then increase 5 von 6 04 12 2006 19 25 Troubleshooting http www tldp org HOWTO NFS HOWTO troubleshooting html 6 von 6 them slowly to a more reasonable value 7 9 nfsd won t start Check the file etc exports and make sure root has read permission Check the binaries and make sure they are executable Make sure your kernel was compiled with NFS server support
10. mounted read write although if it is mounted read only you ought to get a more specific error message If not then you need to re mount with the rw option The second problem has to do with username mappings and is different depending on whether you are trying to do this as root or as a non root user If you are not root then usernames may not be in sync on the client and the server Type id user on both the client and the server and make sure they give the same UID number If they don t then you are having problems with NIS NIS rsync or whatever system you use to sync usernames Check group names to make sure that they match as well Also make sure you are not exporting with the a11_squash option If the user names match then the user has a more general permissions problem unrelated to NFS If you are root then you are probably not exporting with the no_root_squash option check 04 12 2006 19 25 Troubleshooting http www tldp org HOWTO NFS HOWTO troubleshooting html 4 von 6 proc fs nfs exports OF var 1lib nfs xtab on the server and make sure the option is listed In general being able to write to the NFS server as root is a bad idea unless you have an urgent need which is why Linux NFS prevents it by default See Section 6 for details If you have root squashing you want to keep it and you re only trying to get root to have the same permissions on the file that the user nobody should have then remember that it is the s
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