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• Locking a file to verify a single execution of a service. How reliable?

  - by Camilo Díaz

  Hello, I am deploying a little service to an UNIX(AIX) system. I want to check if there is no active instance of that service running when starting it. How reliable is to implement that check like this? Try to acquire a lock on a file (w/ FileChannel) If succeeds, keep lock and continue execution If fails, exit and refuse to run the main body I am aware of software like the Tanuki wrapper, however, I'm longing for a simpler(maybe not portable) solution. Regarding PIDFILE(s): I want to avoid using them if possible, as I don't have administrative rights on the machine, neither knowledge in AIX's shell programming.

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• What is wrong with locking non-static fields? What is the correct way to lock a particular instance?

  - by smartcaveman

  Why is it considered bad practice to lock non-static fields? And, if I am not locking non-static fields, then how do I lock an instance method without locking the method on all other instances of the same or derived class? I wrote an example to make my question more clear. public abstract class BaseClass { private readonly object NonStaticLockObject = new object(); private static readonly object StaticLockObject = new object(); protected void DoThreadSafeAction<T>(Action<T> action) where T: BaseClass { var derived = this as T; if(derived == null) { throw new Exception(); } lock(NonStaticLockObject) { action(derived); } } } public class DerivedClass :BaseClass { private readonly Queue<object> _queue; public void Enqueue(object obj) { DoThreadSafeAction<DerivedClass>(x=>x._queue.Enqueue(obj)); } } If I make the lock on the StaticLockObject, then the DoThreadSafeAction method will be locked for all instances of all classes that derive from BaseClass and that is not what I want. I want to make sure that no other threads can call a method on a particular instance of an object while it is locked.

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• Apache / PHP Begins to Deny SQL Requests after about 2000

  - by Daniel Stern

  We have a web page on our server that we use to run administrative scripts. For example, we might run the script "unenrolStudents()" which runs 5,000 SQL SET commands one after another and sets 5000 student entries in an SQL database to unenrolled. However, we are finding that after running a few thousand queries (it is not totally consistent) we will be "locked out" by our server. SYMPTOMS OF LOCKING OUT: - unable to connect to server with winSCP - opening putty with that connection shows a blank screen (no login / pass) - clearing cookies / cache in chrome does NOT fix locking out - other computers in the office ALSO become locked out - locking out can be triggered with a high frequency of requests (10000 in 1 second) or by less over time (10000 in 500 seconds - this will still cause a lockout even though the frequency is much less) We believe this is a security feature of our own Apache. I know we are using Suhosin but I didn't configure it so I don't know. How can I disable this locking effect so that I can confidently run all my SQL requests and they will go through? Has anyone else dealt with this and found workarounds? Thanks DS

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• GAC locking problem when running deployment

  - by Kieran

  We have a NANT script that uses msbuild to compile our visual studio solutions and deploys the .dlls into the GAC. This works well on our integration/test servers as part of continuous integration, cruise control uses the NANT scripts and every time the dlls are put into the GAC without problem. On our local development machines, where we use subversion/vs.net etc. for development, frequently certain dlls do not make it to the GAC when we run the build. We think we have narrowed this down to visual studio and/or a plug in locking the GAC or the dlls for some reason. Strangely if we run the build a second time all the dlls make it to the GAC. We have added various iisreset's to the NANT script in the hope of releasing the lock but to no avail. Can anyone suggest a good approach to attack this problem? All the best

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• SLES 11 - ocfs2 - Locking does not appear to work

  - by Autobyte

  Hi I have two SLES 11 servers that are SAN attached to a Clarion CX-340. The SAN partition has been formatted with ocfs2 and I have both machines setup in a cluster and the cluster is running (all appears to be normal). I have a small java application as a locking test and when I run the application on both machines at the same time, I should get the lock on one server and the other should refuse the lock since the first already holds a lock on that file but in this case both servers get a lock on the same file. Basically my cluster.conf looks like this: node: ip_port = 7777 ip_address = 192.168.10.121 number = 1 name = osrsles10node1 cluster = osrsles10 node: ip_port = 7777 ip_address = 192.168.10.122 number = 2 name = osrsles10node2 cluster = osrsles10 cluster: node_count = 2 name = osrsles10 Please ask for any other info - I really need these locks to be exclusive to each server. Thanks.

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• How safe is locking the screen?

  - by D Connors

  So, both windows and linux have a pretty useful feature that allows you to leave everything running on the PC while also keeping invaders away by locking the screen. My question is: Say I leave my laptop with the screen locked while I go get a donnut, and then it gets stolen. Assuming the thief has access to whatever software he needs, how easy/hard would it be for him to access my (currently logged-in) account? Now let me be clear. I'm not asking if he can access the data on the harddrive. I know he can, and that issue would go under data encryption, which is not my question here. I'm focusing on how hard would it be to get around the "Insert Password" screen, and have full access to my account. I'm looking for answers regarding both OS's; but, if needed, assume Ubuntu. Thank you.

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• Windows 7 Locking up Randomly

  - by Michael Moore

  I've got a Windows 7 machine that is locking up randomly. It can be in the first thirty seconds, or it can be hours later. There is nothing specific I can find that is running when it happens. When it locks, the screen doesn't change, but nothing moves. The waiting icon stops, the mouse stops, keyboard doesn't work, etc. I've even tried the crash on ctrl-scrl registry hack, and it won't even dump the kernel. I've run hardware diagnostics on the RAM and it doesn't find any problems. I would think it is a hardware issue, but on this exact same machine, I can run 64 Bit Ubuntu and it has zero problems. I've even tried reinstalling Windows7 from scratch, and it still happens. Anyone have any ideas? Any good diagnostic tools to recommend? Thanks! Michael

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• Locking down remote desktop using AD GPO

  - by Brettski

  I am currently locking down a companies remote desktop access via a VPN. What I need to do is disable remote printing, file transfer and clipboard via active directory for the workstations that will be accessed. I am having trouble figuring out which GPO's are used to restrict this. My basic approach is to restrict VPN users to port 3389 so the will be able to access their work computers remotely but nothing else (I will look into layer 7 scanning later). With this I want to ensure they are unable to transfer and data via files, printing or the clipboard. The environment is Windows Server 2003

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• MySQLDump without locking the tables

  - by Raul Singahn

  It seems that if you have many tables, you can only perform a MySQLDump without locking them all, otherwise you can an error. What are the side effects of performing a MySQLDump without locking all the tables; Is the DB snapshot I get this way, consistent? Do I have any other alternative for getting a backup of a MySQL DB with many tables?

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• Compaq R4000 laptop randomly locking up

  - by Josh

  I have a Compaq R4000 laptop with 2GB of RAM, running Ubuntu Linux 9.10. It is randomly locking up on me, approximately once every two days. I have a second partition with Windows XP Home installed, and I have had the system lock up in XP as well, meaning I believe this is a hardware issue. I have run two passes of Memtest86+ with no errors. The system has a fan that has died, so I initially suspected overheating. However the system just locked up on me while I was in the middle of typing a script to warn me / shut down if the temperature was too high. When the lockup happened the temperature was 88°F, so I am now starting to believe that may not be the issue. When the system locks up, I cannot SSH in nor ping it. Nothing shows in syslog when I reboot. I have configured it to send syslog messages to a local server as well and no messages appear on that server when the lockup happens. I am open to any and all advice!

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• Make a snapshot of a live mySQL database with myISAM & innoDB tables without locking

  - by Artem

  We have a live database in production where we are running out of space on the server. So I would like to transfer to a new server without any downtime (or as little downtime as possible). In general, I would also like to have a hot failover copy of the database available. I would like to use replication to get all of the data copied to the new machine, and then at some point flip a switch and have that new machine become the master (normal failover scenario). My problem is that I am not sure how to initialize replication without locking the db to make the initial snapshot I will use? Is there any way to do this? I know I could do it using single-transaction if I was using innoDB, but very unfortunately we have some myISAM tables in there (in fact the largest 150GB table is myISAM and I want to switch it to InnoDB but I can't do it until I have more space & a hot copy to switch to). Any ideas? Is there some way to make such a snapshot? Or is there alternatively a way to get replication to "catch up" without an snapshot for initialization?

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• SQL Server Read Locking behavior

  - by Charles Bretana

  When SQL Server Books online says that "Shared (S) locks on a resource are released as soon as the read operation completes, unless the transaction isolation level is set to repeatable read or higher, or a locking hint is used to retain the shared (S) locks for the duration of the transaction." Assuming we're talking about a row-level lock, with no explicit transaction, at default isolation level (Read Committed), what does "read operation" refer to? The reading of a single row of data? The reading of a single 8k IO Page ? or until the the complete Select statement in which the lock was created has finished executing, no matter how many other rows are involved? NOTE: The reason I need to know this is we have a several second read-only select statement generated by a data layer web service, which creates page-level shared read locks, generating a deadlock due to conflicting with row-level exclusive update locks from a replication prcoess that keeps the server updated. The select statement is fairly large, with many sub-selects, and one DBA is proposing that we rewrite it to break it up into multiple smaller statements (shorter running pieces), "to cut down on how long the locks are held". As this assumes that the shared read locks are held till the complete select statement has finished, if that is wrong (if locks are released when the row, or the page is read) then that approach would have no effect whatsoever....

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• NFS-shared file-system is locking up

  - by fredden

  Our NFS-shared file-system is locking up. Please feel free to ask any questions you feel relevant. :) At the time, there are a lot of processes in "disk sleep" state, and the load averages on our machines sky-rocket. The machines are responsive on SSH, but our the majority of our websites (apache+mod_php) just hang, as does our email system (exim+dovecot). Any websites which don't require write access to the file-system continue to operate. The load averages continue to rise until some kind of time-out is reached, but for at least 10-15 minutes. I've seen load averages over 800, yet the machines are still responsive for actions which don't require writing to the shared file-system. I've been investigating a variety of options, which have all turned out to be red-herrings: nagios, proftpd, bind, cron tasks. I'm seeing these messages in the file server's system log: Jul 30 09:37:17 fs0 kernel: [1810036.560046] statd: server localhost not responding, timed out Jul 30 09:37:17 fs0 kernel: [1810036.560053] nsm_mon_unmon: rpc failed, status=-5 Jul 30 09:37:17 fs0 kernel: [1810036.560064] lockd: cannot monitor node2 Jul 30 09:38:22 fs0 kernel: [1810101.384027] statd: server localhost not responding, timed out Jul 30 09:38:22 fs0 kernel: [1810101.384033] nsm_mon_unmon: rpc failed, status=-5 Jul 30 09:38:22 fs0 kernel: [1810101.384044] lockd: cannot monitor node0 Software involved: VMWare, Debian lenny (64bit), ancient Red Hat (32 bit) (version 7 I believe), Debian etch (32bit) NFS, apache2+mod_php, exim, dovecot, bind, amanda, proftpd, nagios, cacti, drbd, heartbeat, keepalived, LVS, cron, ssmtp, NIS, svn, puppet, memcache, mysql, postgres Joomla!, Magento, Typo3, Midgard, Symfony, custom php apps

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• Disadvantages of MySQL Row Locking

  - by Nyxynyx

  I am using row locking (transactions) in MySQL for creating a job queue. Engine used is InnoDB. SQL Query START TRANSACTION; SELECT * FROM mytable WHERE status IS NULL ORDER BY timestamp DESC LIMIT 1 FOR UPDATE; UPDATE mytable SET status = 1; COMMIT; According to this webpage, The problem with SELECT FOR UPDATE is that it usually creates a single synchronization point for all of the worker processes, and you see a lot of processes waiting for the locks to be released with COMMIT. Question: Does this mean that when the first query is executed, which takes some time to finish the transaction before, when the second similar query occurs before the first transaction is committed, it will have to wait for it to finish before the query is executed? If this is true, then I do not understand why the row locking of a single row (which I assume) will affect the next transaction query that would not require reading that locked row? Additionally, can this problem be solved (and still achieve the effect row locking does for a job queue) by doing a UPDATE instead of the transaction? UPDATE mytable SET status = 1 WHERE status IS NULL ORDER BY timestamp DESC LIMIT 1

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• Unit Testing Hibernate's Optimistic Locking (within Spring)

  - by Michal Bachman

  I'd like to write a unit test to verify that optimistic locking is properly set up (using Spring and Hibernate). I'd like to have the test class extend Spring's AbstractTransactionalJUnit4SpringContextTests. What I want to end up with is a method like this: @Test (expected = StaleObjectStateException.class) public void testOptimisticLocking() { A a = getCurrentSession().load(A.class, 1); a.setVersion(a.getVersion()-1); getCurrentSession().saveOrUpdate(a); getCurrentSession().flush(); fail("Optimistic locking does not work"); } This test fails. What do you recommend as a best practice? The reason I am trying to do this is that I want to transfer the version to the client (using a DTO). I want to prove that when the DTO is sent back to the server and merged with a freshly loaded entity, saving that entity will fail if it's been updated by somebody else in the meantime.

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• Why use SyncLocks in .NET for simple operations when Interlocked class is available?

  - by rwmnau

  I've been doing simple multi-threading in VB.NET for a while, and have just gotten into my first large multi-threaded project. I've always done everything using the Synclock statement because I didn't think there was a better way. I just learned about the Interlocked Class - it makes it look as though all this: Private SomeInt as Integer Private SomeInt_LockObject as New Object Public Sub IntrementSomeInt Synclock SomeInt_LockObject SomeInt += 1 End Synclock End Sub Can be replaced with a single statement: Interlocked.Increment(SomeInt) This handles all the locking internally and modifies the number. This would be much simpler than writing my own locks for simple operations (longer-running or more complicated operations obviously still need their own locking). Is there a reason why I'd rolling my own locking, using dedicated locking objects, when I can accomplish the same thing using the Interlocked methods?

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• DataReader Behaviour With SQL Server Locking

  - by Graham

  We are having some issues with our data layer when large datasets are returned from a SQL server query via a DataReader. As we use the DataReader to populate business objects and serialize them back to the client, the fetch can take several minutes (we are showing progress to the user :-)), but we've found that there's some pretty hard-core locking going on on the affected tables which is causing other updates to be blocked. So I guess my slightly naive question is, at what point are the locks which are taken out as a result of executing the query actually relinquished? We seem to be finding that the locks are remaining until the last row of the DataReader has been processed and the DataReader is actually closed - does that seem correct? A quick 101 on how the DataReader works behind the scenes would be great as I've struggled to find any decent information on it. I should say that I realise the locking issues are the main concern but I'm just concerned with the behaviour of the DataReader here.

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• Record locking problem between linux and Windows

  - by PabloG

  I need to run a bunch of old DOS FoxPro / Clipper applications in linux under DOSEMU. The programs access their "databases" located on a network server (could be a Windows or Linux server) Actually, the programs ran fine, but I cannot manage to make the record locking work as supposed: I can run a program in two terminals (or the server and any terminal for instance) and lock the same record in both. Now, I'm using Tiny Core Linux as terminal and Windows XP as server, accesing the shared files via CIFS and the latest DOSEMU (1.4.0), but I tried with various combinations of server (Ubuntu 7 to 9, Damn Small Linux, XP) <- protocol (CIFS, samba, various versions of smbclient) <- client (same as server) with no luck I tried to configure the server part to work without oplocks in samba (after reading the entire O'Reilly Samba book locking chapter in http://oreilly.com/catalog/samba/chapter/book/ch05_05.html ) and in XP (\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\UseOpportunisticLocking = 0) but the problem persist. Any ideas? TIA, Pablo

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• Do MySQL Locked Tables affect related Views?

  - by CogitoErgoSum

  So after reading http://stackoverflow.com/questions/1415602/performance-in-pdo-php-mysql-transaction-versus-direct-execution in regards to performance issues I was thinking about I did some research on locking tables in MySQL. On http://dev.mysql.com/doc/refman/5.0/en/table-locking.html Table locking enables many sessions to read from a table at the same time, but if a session wants to write to a table, it must first get exclusive access. During the update, all other sessions that want to access this particular table must wait until the update is done. This part struck me particularly becuase most of our queries will be updates rather than inserts. I was wondering if one created a table called foo on which all updates/inserts were carried out and then a view called foo_view (A copy of foo, or perhaps foo and a linkage of several other tables plus foo) on which all selects occured, would this locking issue still occur? That is, would SELECT quries on foo_view still have to wait for an update to finish on foo?

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• What is the best WebDAV client for Windows?

  - by dr0ne

  The support of locking will be preferred.

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• What privilege level is required on a Windows client workstation on an ActiveDomain to break file lo

  - by Mike Burton

  I'm not sure if I should be asking this here or on StackOverflow, but here goes: I'm part of a team maintaining a document management application, and I'm trying to figure out Windows file locking permissions. We use a utility somebody downloaded years ago called psunlock to remotely close all locks on a file. We recently discovered that this does not work across different domains on our VPN. A little bit of digging lead me to the samba manual's discussion of file locking. I still don't really "get it", though. Does anyone have any insight to share into how the process of locking and breaking locks on files works in a network context? My thinking is that privileges are required both on the file appliance and on the client workstations which hold locks. Is that accurate? Can anyone give a more specific version? Ideally I'm looking for something along the lines of A user must have privilege level X in order to break locks held from a client workstation. In practice I'd be happy with a hotlink to a good white paper on the subject.

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• Follow-up Answers for my Australia Classes

  - by Kalen Delaney

  I was out of the country for the last two weeks of March, delivering classes in Brisbane and Sydney, which were organized by WardyIT . It was a great visit and there were 24 terrific students! As is sometimes (perhaps often?) the case, there were questions posed that I couldn’t answer during class, so here are a couple of follow-up answers. 1. I brought up the fact that SQLS 2012 generates a warning message when there are ‘too many’ Virtual Log Files (VLFs) in a database. (It turns out the message...(read more)

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• Apache MaxClients reaching max and locking the server

  - by Rodrigo Sieiro

  Hi. I currently have an Apache2 server running with mpm-prefork and mod_php on a OpenVZ VPS with 512M real / 1024M burstable RAM (no swap). After running some tests, I found that the maximum process size Apache gets is 23M, so I've set MaxClients to 25 (23M x 25 = 575 MB, ok for me). I decided to run some load tests on my server, and the results left me puzzled. I'm using ab on my desktop machine requesting the main page from a wordpress blog. When I run ab with 24 concurrent connections, everything seems fine. Sure, CPU goes up, free RAM goes down, and the result is about 2-3s response time per request. But if I run ab with 25 concurrent connections (my server limit), Apache just hangs after a couple of seconds. It starts processing the requests, then it stops responding, CPU goes back to 100% idle and ab times out. Apache log says it reached MaxClients. When this happens, Apache keeps itself locked up with 25 running processes (they're all in "W" if I check server status) and only after the TimeOut setting the processes start to die and the server starts responding again (in my case it's set to 45). My question: is that expected behaviour? Why Apache just dies when it reaches MaxClients? If it works with 24 connections, shouldn't it work with 25, just taking maybe more time to respond each request and queueing up the rest? It sounds kinda strange to me that any kid running ab can alone kill a webserver just by setting the concurrent connections to the servers MaxClients.

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• Apache reaching MaxClients and locking the server

  - by Rodrigo Sieiro

  Hi. I currently have an Apache2 server running with mpm-prefork and mod_php on a OpenVZ VPS with 512M real / 1024M burstable RAM (no swap). After running some tests, I found that the maximum process size Apache gets is 23M, so I've set MaxClients to 25 (23M x 25 = 575 MB, ok for me). I decided to run some load tests on my server, and the results left me puzzled. I'm using ab on my desktop machine requesting the main page from a wordpress blog. When I run ab with 24 concurrent connections, everything seems fine. Sure, CPU goes up, free RAM goes down, and the result is about 2-3s response time per request. But if I run ab with 25 concurrent connections (my server limit), Apache just hangs after a couple of seconds. It starts processing the requests, then it stops responding, CPU goes back to 100% idle and ab times out. Apache log says it reached MaxClients. When this happens, Apache keeps itself locked up with 25 running processes (they're all in "W" if I check server status) and only after the TimeOut setting the processes start to die and the server starts responding again (in my case it's set to 45). My question: is that expected behaviour? Why Apache just dies when it reaches MaxClients? If it works with 24 connections, shouldn't it work with 25, just taking maybe more time to respond each request and queueing up the rest? It sounds kinda strange to me that any kid running ab can alone kill a webserver just by setting the concurrent connections to the servers MaxClients.

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• IPFW not locking people out

  - by Cole

  I've had some brute-forcing of my ssh connection recently, so I got fail2ban to hopefully prevent that. I set it up, and started testing it out by giving wrong passwords on my computer. (I have physical access to the server if I need to unblock myself) However, it never stops me from entering passwords. I see in /var/log/fail2ban.log that fail2ban kicked in and banned me, and there's a ipfw entry for my IP, but I'm not locked out. I've changed the configuration around, and then tried just using the ipfw command myself, but nothing seems to lock me out. I've tried the following blocks: 65300 deny tcp from 10.0.1.30 to any in 65400 deny ip from 10.0.1.30 to any 65500 deny tcp from 10.0.1.30 to any My firewall setup has a "allow ip from any to any" rule after these though, maybe that's the problem? I'm using Mac OS 10.6 (stock ipfw, it doesn't seem to have a --version flag) Thanks in advance.

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