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  • Kernel module for /proc

    - by sb2367
    How to write a kernel module that creates a directory in /proc named mymod and a file in it name is mymodfile. This file should accept a number ranged from 1 to 3 when written into it and return the following messages when read based on the number already written into it: • 1: Current system time (in microseconds precision) • 2: System uptime • 3: Number of processes currently in the system “The Output” root@Paradise# echo 1 > /proc/mymod/mymodfile root@Paradise# cat /proc/mymod/mymodfile 08:30:24 342us root@Paradise# echo 2 > /proc/mymod/mymodfile root@Paradise# cat /proc/mymod/mymodfile up 1 day, 8 min root@Paradise# echo 3 > /proc/mymod/mymodfile root@Paradise# cat /proc/mymod/mymodfile process count: 48 please give me some hint how to write a kernel modules and how to compile and install it .

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  • Maximum number of files in one ext3 directory while still getting acceptable performance?

    - by knorv
    I have an application writing to an ext3 directory which over time has grown to roughly three million files. Needless to say, reading the file listing of this directory is unbearably slow. I don't blame ext3. The proper solution would have been to let the application code write to sub-directories such as ./a/b/c/abc.ext rather than using only ./abc.ext. I'm changing to such a sub-directory structure and my question is simply: roughly how many files should I expect to store in one ext3 directory while still getting acceptable performance? What's your experience? Or in other words; assuming that I need to store three million files in the structure, how many levels deep should the ./a/b/c/abc.ext structure be? Obviously this is a question that cannot be answered exactly, but I'm looking for a ball park estimate.

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  • Boost program will not working on Linux

    - by Martin Lauridsen
    Hi SOF, I have this program which uses Boost::Asio for sockets. I pretty much altered some code from the Boost examples. The program compiles and runs just like it should on Windows in VS. However, when I compile the program on Linux and run it, I get a Segmentation fault. I posted the code here The command I use to compile it is this: c++ -I/appl/htopopt/Linux_x86_64/NTL-5.4.2/include -I/appl/htopopt/Linux_x86_64/boost_1_43_0/include mpqs.cpp mpqs_polynomial.cpp mpqs_host.cpp -o mpqs_host -L/appl/htopopt/Linux_x86_64/NTL-5.4.2/lib -lntl -L/appl/htopopt/Linux_x86_64/gmp-4.2.1/lib -lgmp -lm -L/appl/htopopt/Linux_x86_64/boost_1_43_0/lib -lboost_system -lboost_thread -static -lpthread By commenting out code, I have found out that I get the Segmentation fault due to the following line: boost::asio::io_service io_service; Can anyone provide any assistance, as to what may be the problem (and the solution)? Thanks! Edit: I tried changing the program to a minimal example, using no other libraries or headers, just boost/asio.hpp: #define DEBUG 0 #include <boost/asio.hpp> int main(int argc, char* argv[]) { boost::asio::io_service io_service; return 0; } I also removed other library inclusions and linking on compilation, however this minimal example still gives me a segmentation fault.

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  • NULL pointer dereference in swiotlb_unmap_sg_attrs() on disk IO

    - by Inductiveload
    I'm getting an error I really don't understand when reading or writing files using a PCIe block device driver. I seem to be hitting an issue in swiotlb_unmap_sg_attrs(), which appears to be doing a NULL dereference of the sg pointer, but I don't know where this is coming from, as the only scatterlist I use myself is allocated as part of the device info structure and persists as long as the driver does. There is a stacktrace to go with the problem. It tends to vary a bit in exact details, but it always crashes in swiotlb_unmap_sq_attrs(). I think it's likely I have a locking issue, as I am not sure how to handle the locks around the IO functions. The lock is already held when the request function is called, I release it before the IO functions themselves are called, as they need an (MSI) IRQ to complete. The IRQ handler updates a "status" value, which the IO function is waiting for. When the IO function returns, I then take the lock back up and return to request queue handling. The crash happens in blk_fetch_request() during the following: if (!__blk_end_request(req, res, bytes)){ printk(KERN_ERR "%s next request\n", DRIVER_NAME); req = blk_fetch_request(q); } else { printk(KERN_ERR "%s same request\n", DRIVER_NAME); } where bytes is updated by the request handler to be the total length of IO (summed length of each scatter-gather segment).

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  • Why my linux signal handler run only once

    - by Henry Fané
    #include <iostream> #include <signal.h> #include <fenv.h> #include <string.h> void signal_handler(int sig, siginfo_t *siginfo, void* context) { std::cout << " signal_handler " << fetestexcept(FE_ALL_EXCEPT) << std::endl; throw "exception"; } void divide() { float a = 1000., b = 0., c, f = 1e-300; c = a / b; std::cout << c << " and f = " << f << std::endl; } void init_sig_hanlder() { feenableexcept(FE_ALL_EXCEPT); struct sigaction sa, initial_sa; sa.sa_sigaction = &signal_handler ; sigemptyset( &sa.sa_mask ) ; sa.sa_flags = SA_SIGINFO; // man sigaction(3) // allows for void(*)(int,siginfo_t*,void*) handler sigaction(SIGFPE, &sa, &initial_sa); } int main(int argc, char** argv) { init_sig_hanlder(); while(true) { try { sleep(1); divide(); } catch(const char * a) { std::cout << "Exception in catch: " << a << std::endl; } catch(...) { std::cout << "Exception in ..." << std::endl; } } return 0; } Produce the following results on Linux/g++4.2: signal_handler 0 Exception in catch: exception inf and f = 0 inf and f = 0 inf and f = 0 inf and f = 0 So, signal handler is executed the first time but the next fp exception does not trigger the handler again. Where am I wrong ?

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  • Help Installing phpMyAdmin on Linux Server

    - by Joe Majewski
    I constantly get this error when attempting to view index.php in the phpMyAdmin folder I have setup: Cannot start session without errors, please check errors given in your PHP and/or webserver log file and configure your PHP installation properly. I am using subversion with three co-workers and I am trying to install this on my repository, which is at /svni3/myusername/intranet/ on our linux development server. I do have shell access so I would be able to install it somewhere else if that may be causing the problem. My config.inc.php file looks like this (only the things I changed): $cfg['blowfish_secret'] = 'blah'; $cfg['Servers'][$i]['auth_type'] = 'cookie'; //$cfg['Servers'][$i]['user'] = 'username'; //$cfg['Servers'][$i]['password'] = 'password'; $cfg['Servers'][$i]['host'] = 'localhost'; Other helpful information??? When I ping localhost it works. When I run the command "ls -l /var/lib/php": drwxrwx--- 2 root apache 4096 2009-04-17 02:31 session If there's anything else that may be helpful let me know; this has been plaguing me for a few hours now.

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  • sysklogd ignores my log facilities

    - by Synther Lawrence
    I'm using sysklogd 1.5.5. All I want is to get local0 entries in /var/log/vr file. My conf: *.*;local0.none /var/log/messages local0.* /var/log/vr When I do logger -p local0.info "local0 test from logger" the message appear in /var/log/vr file. That's ok. But the following sends message to /var/log/messages instead of /var/log/vr: #include <stdlib.h> #include <syslog.h> int main(int argc, char const* argv[]) { openlog(NULL, LOG_PID, LOG_LOCAL0); syslog(LOG_INFO, "local0 test from app\n"); closelog(); return 0; } Where am I wrong?

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  • CSV Parser works in windows, not linux.

    - by ladookie
    I'm parsing a CSV file that looks like this: E1,E2,E7,E8,,, E2,E1,E3,,,, E3,E2,E8,,, E4,E5,E8,E11,,, I store the first entry in each line in a string, and the rest go in a vector of strings: while (getline(file_input, line)) { stringstream tokenizer; tokenizer << line; getline(tokenizer, roomID, ','); vector<string> aVector; while (getline(tokenizer, adjRoomID, ',')) { if (!adjRoomID.empty()) { aVector.push_back(adjRoomID); } } Room aRoom(roomID, aVector); rooms.addToTail(aRoom); } In windows this works fine, however in Linux the first entry of each vector mysteriously loses the first character. For Example in the first iteration through the while loop: roomID would be E1 and aVector would be 2 E7 E8 then the second iteration: roomID would be E2 and aVector would be 1 E3 Notice the missing E's in the first entry of aVector. when I put in some debugging code it appears that it is initially being stored correctly in the vector, but then something overwrites it. Kudos to whoever figures this one out. Seems bizarre to me. rooms is declared as such: DLList<Room> rooms where DLList stands for Doubly-Linked list.

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  • Java socket bug on linux (0xFF sent, -3 received)

    - by Marius
    While working on a WebSocket server in Java I came across this strange bug. I've reduced it down to two small java files, one is the server, the other is the client. The client simply sends 0x00, the string Hello and then 0xFF (per the WebSocket specification). On my windows machine, the server prints the following: Listening byte: 0 72 101 108 108 111 recieved: 'Hello' While on my unix box the same code prints the following: Listening byte: 0 72 101 108 108 111 -3 Instead of receiving 0xFF it gets -3, never breaks out of the loop and never prints what it has received. The important part of the code looks like this: byte b = (byte)in.read(); System.out.println("byte: "+b); StringBuilder input = new StringBuilder(); b = (byte)in.read(); while((b & 0xFF) != 0xFF){ input.append((char)b); System.out.print(b+" "); b = (byte)in.read(); } inputLine = input.toString(); System.out.println("recieved: '" + inputLine+"'"); if(inputLine.equals("bye")){ break; } I've also uploaded the two files to my server: Server.java Client.java My Windows machine is running windows 7 and my Linux machine is running Debian

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  • C++: Help with cin difference between Linux and Windows

    - by Krashman5k
    I have a Win32 console program that I wrote and it works fine. The program takes input from the user and performs some calculations and displays the output - standard stuff. For fun, I am trying to get the program to work on my Fedora box but I am running into an issue with clearing cin when the user inputs something that does not match my variable type. Here is the code in question: void CParameter::setPrincipal() { double principal = 0.0; cout << endl << "Please enter the loan principal: "; cin >> principal; while(principal <= 0) { if (cin.fail()) { cin.clear(); cin.ignore(INT_MAX, '\n'); } else { cout << endl << "Plese enter a number greater than zero. Please try again." << endl; cin >> principal; } } m_Parameter = principal; } This code works in Windows. For example, if the user tries to enter a char data type (versus double) then the program informs the user of the error, resets cin, and allows the user another opportunity to enter a valid value. When I move this code to Fedora, it compiles fine. When I run the program and enter an invalid data type, the while loop never breaks to allow the user to change the input. My questions are; how do I clear cin when invalid data is inputted in the Fedora environment? Also, how should I write this code so it will work in both environments (Windows & Linux)? Thanks in advance for your help!

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  • malloc in kernel

    - by yoavstr
    when i try to malloc at kernel mod i get screamed by the compiler : res=(ListNode*)malloc(sizeof(ListNode)); and the compiler is screaming : /root/ex3/ex3mod.c:491: error: implicit declaration of function ‘malloc’ what should i do ?

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  • compile error:c language in telnet(linux)

    - by lilyrose07
    #include<stdio.h> #include<unistd.h> #include<stdlib.h> #include<pthread.h> int count=0; void *thread_function(void *arg) { while(count<10) { if(count%2==1) { count++; } else {sleep(1);} } } int main(int argc,int *argv) { int res; pthread_t a_thread[2]; void *thread_result; int n; while(count<10) { if(count%2==0) {printf("%d",count); count++; } else{sleep(1);} } for(n=0;n<2;n++) { pthread_create(&(a_thread[n]),NULL,thread_function,NULL); } while(count==9) {pthread_join(a_thread[0],&thread_result); } while(count==10) { pthread_join(a_thread[1],&thread_result); } printf("%d",count); return 0; } in telnet,linux i write gcc za.c error list: undefined reference to pthread_create,pthread_join in function 'main' //why??

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  • String manipulation in Linux kernel module

    - by user577066
    I am having a hard time in manipulating strings while writing module for linux. My problem is that I have a int Array[10] with different values in it. I need to produce a string to be able send to the buffer in my_read procedure. If my array is {0,1,112,20,4,0,0,0,0,0} then my output should be: 0:(0) 1:-(1) 2:-------------------------------------------------------------------------------------------------------(112) 3:--------------------(20) 4:----(4) 5:(0) 6:(0) 7:(0) 8:(0) 9:(0) when I try to place the above strings in char[] arrays some how weird characters end up there here is the code int my_read (char *page, char **start, off_t off, int count, int *eof, void *data) { int len; if (off > 0){ *eof =1; return 0; } /* get process tree */ int task_dep=0; /* depth of a task from INIT*/ get_task_tree(&init_task,task_dep); char tmp[1024]; char A[ProcPerDepth[0]],B[ProcPerDepth[1]],C[ProcPerDepth[2]],D[ProcPerDepth[3]],E[ProcPerDepth[4]],F[ProcPerDepth[5]],G[ProcPerDepth[6]],H[ProcPerDepth[7]],I[ProcPerDepth[8]],J[ProcPerDepth[9]]; int i=0; for (i=0;i<1024;i++){ tmp[i]='\0';} memset(A, '\0', sizeof(A));memset(B, '\0', sizeof(B));memset(C, '\0', sizeof(C)); memset(D, '\0', sizeof(D));memset(E, '\0', sizeof(E));memset(F, '\0', sizeof(F)); memset(G, '\0', sizeof(G));memset(H, '\0', sizeof(H));memset(I, '\0', sizeof(I));memset(J, '\0', sizeof(J)); printk("A:%s\nB:%s\nC:%s\nD:%s\nE:%s\nF:%s\nG:%s\nH:%s\nI:%s\nJ:%s\n",A,B,C,D,E,F,G,H,I,J); memset(A,'-',sizeof(A)); memset(B,'-',sizeof(B)); memset(C,'-',sizeof(C)); memset(D,'-',sizeof(D)); memset(E,'-',sizeof(E)); memset(F,'-',sizeof(F)); memset(G,'-',sizeof(G)); memset(H,'-',sizeof(H)); memset(I,'-',sizeof(I)); memset(J,'-',sizeof(J)); printk("A:%s\nB:%s\nC:%s\nD:%s\nE:%s\nF:%s\nG:%s\nH:%s\nI:%s\nJ:%\n",A,B,C,D,E,F,G,H,I,J); len = sprintf(page,"0:%s(%d)\n1:%s(%d)\n2:%s(%d)\n3:%s(%d)\n4:%s(%d)\n5:%s(%d)\n6:%s(%d)\n7:%s(%d)\n8:%s(%d)\n9:%s(%d)\n",A,ProcPerDepth[0],B,ProcPerDepth[1],C,ProcPerDepth[2],D,ProcPerDepth[3],E,ProcPerDepth[4],F,ProcPerDepth[5],G,ProcPerDepth[6],H,ProcPerDepth[7],I,ProcPerDepth[8],J,ProcPerDepth[9]); return len; }

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  • IBM Thinkpad 240 - Best way to boot from floppy to USB - Best Linux for 300 MHz 128 MB RAM 800x600 s

    - by zillion
    Mostly I still have that old 'ultraportable' laptop that is mostly like a pre-netbook era laptop and a friend and programmer needs a computer because the one he was using just broke and he has to wait until the new one arrive in 4-6 weeks ... This laptop has no LAN connection and CD-ROM so be prepared for a real challenge! All hardware is well supported on Windows XP (included drivers on the Windows XP CD) and on Linux out-of-the-box (but the screen need a special configuration.) Mostly any Linux that will work well with Skype (USB or regular headset), any MSN client and a text writer for code will do. What I have tested so far: Slitaz 2 don't boot because the floppy of GRUB4DOS don't see the USB drive (fully working and tested on my regular laptop), Damn Small Linux was working but was needing a special screen configuration that I don't remember (in the boot options of the floppy) and now I'm thinking about Puppy Linux that is seen to work totally out of the box with it but I will need an old Puppy version (1 or 2 I think) and the Wakepup floppy ... If you got some ideas to help or to try I'm open!

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  • What is the difference between the Linux and Linux LVM partition type?

    - by ujjain
    Fdisk shows multiple partition types. What is the difference between choosing 83) Linux and 8e) Linux LVM? Choosing 83) Linux also works fine for using LVM, even creating a physical volume on /dev/sdb without a partition table works. Does picking a partition type in fdisk really matter? What is the difference in picking Linux or Linux LVM as partition type? [root@tst-01 ~]# fdisk /dev/sdb WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u'). Command (m for help): l 0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris 1 FAT12 39 Plan 9 82 Linux swap / So c1 DRDOS/sec (FAT- 2 XENIX root 3c PartitionMagic 83 Linux c4 DRDOS/sec (FAT- 3 XENIX usr 40 Venix 80286 84 OS/2 hidden C: c6 DRDOS/sec (FAT- 4 FAT16 <32M 41 PPC PReP Boot 85 Linux extended c7 Syrinx 5 Extended 42 SFS 86 NTFS volume set da Non-FS data 6 FAT16 4d QNX4.x 87 NTFS volume set db CP/M / CTOS / . 7 HPFS/NTFS 4e QNX4.x 2nd part 88 Linux plaintext de Dell Utility 8 AIX 4f QNX4.x 3rd part 8e Linux LVM df BootIt 9 AIX bootable 50 OnTrack DM 93 Amoeba e1 DOS access a OS/2 Boot Manag 51 OnTrack DM6 Aux 94 Amoeba BBT e3 DOS R/O b W95 FAT32 52 CP/M 9f BSD/OS e4 SpeedStor c W95 FAT32 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi eb BeOS fs e W95 FAT16 (LBA) 54 OnTrackDM6 a5 FreeBSD ee GPT f W95 Ext'd (LBA) 55 EZ-Drive a6 OpenBSD ef EFI (FAT-12/16/ 10 OPUS 56 Golden Bow a7 NeXTSTEP f0 Linux/PA-RISC b 11 Hidden FAT12 5c Priam Edisk a8 Darwin UFS f1 SpeedStor 12 Compaq diagnost 61 SpeedStor a9 NetBSD f4 SpeedStor 14 Hidden FAT16 <3 63 GNU HURD or Sys ab Darwin boot f2 DOS secondary 16 Hidden FAT16 64 Novell Netware af HFS / HFS+ fb VMware VMFS 17 Hidden HPFS/NTF 65 Novell Netware b7 BSDI fs fc VMware VMKCORE 18 AST SmartSleep 70 DiskSecure Mult b8 BSDI swap fd Linux raid auto 1b Hidden W95 FAT3 75 PC/IX bb Boot Wizard hid fe LANstep 1c Hidden W95 FAT3 80 Old Minix be Solaris boot ff BBT 1e Hidden W95 FAT1 Command (m for help):

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  • How to use Timer broadcast on Multi-Processor system with linux 3.10?

    - by kevin.ji
    Hardware: ARM Cortex-A9 * 2 Software: linux-3.10.0 The platform has 2 cores of arm cortex-a9. Item CONFIG_LOCAL_TIMERS is not set in linux menuconfig. I want to use only one hardware timer to supply tick for all cpu. Interrupts looks like: CPU0 CPU1 57: 6697 0 GIC timer 81: 213 0 GIC uart-pl011 103: 0 0 GIC gmac0 104: 0 0 GIC gmac1 IPI0: 0 1 CPU wakeup interrupts IPI1: 0 0 Timer broadcast interrupts IPI2: 967 866 Rescheduling interrupts IPI3: 0 0 Function call interrupts IPI4: 1 2 Single function call interrupts IPI5: 0 0 CPU stop interrupts IPI6: 0 0 CPU backtrace Err: 0 Timer broadcast interrupts counter does not add. And it looks like that cpu1 does not work at all.But this method works well with linux-3.4, and the interrupt info looks as below in linux-3.4: # cat /proc/interrupts CPU0 CPU1 57: 8596 0 GIC timer 81: 91 0 GIC uart-pl011 103: 0 0 GIC gmac0 104: 0 0 GIC gmac1 IPI0: 0 8560 Timer broadcast interrupts IPI1: 884 1020 Rescheduling interrupts IPI2: 0 0 Function call interrupts IPI3: 0 6 Single function call interrupts IPI4: 0 0 CPU stop interrupts IPI5: 0 0 CPU backtrace Err: 0 The count of Timer broadcast interrupts is adding. And all of cpus work well. I don't know why. Any answer is welcome. :)

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  • Can't mount Linux usd disk. It just create /dev/sg device but no /dev/sd

    - by MTilsted
    I have a Corsair R60 ssd disk which is a disk with both sata and usb connectors. But the usb thing seems to be a bit non-standard, or maybe its just my fedora linux. When I insert the disk using a usb cabel to a running Fedora 14 linux system, a device called /dev/sg3 is added but that is all. No new /dev/sd* device is created so I can't mount the disk. If I look at cat /proc/scsi/sg/device_strs I get ATA Hitachi HTS54321 FB2O HL-DT-ST DVDRAM GSA-T50N RP05 Seagate Desktop 0130 Corsair CSSD-R60GB2 So the disk is there. (The last entry) but my linux will for some reason not see it as a usb hard disk. When I insert other usb disks they work fine. It is only this specific disk which causes problems. I have tried on 3 different computers with the same result. A hint to the problem may be that if I add the disk to a windows system(With usb) the disk is called "A fixed disk" and not a portable disk as expected. The disk works fine with linux If i connect it with the sata cabel, but I would really like to have it working with usb too. (To mount it on computers without sata).

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  • Can't mount Linux usb disk. It just create /dev/sg device but no /dev/sd

    - by MTilsted
    I have a Corsair R60 ssd disk which is a disk with both sata and usb connectors. But the usb thing seems to be a bit non-standard, or maybe its just my fedora linux. When I insert the disk using a usb cabel to a running Fedora 14 linux system, a device called /dev/sg3 is added but that is all. No new /dev/sd* device is created so I can't mount the disk. If I look at cat /proc/scsi/sg/device_strs I get ATA Hitachi HTS54321 FB2O HL-DT-ST DVDRAM GSA-T50N RP05 Seagate Desktop 0130 Corsair CSSD-R60GB2 So the disk is there. (The last entry) but my linux will for some reason not see it as a usb hard disk. When I insert other usb disks they work fine. It is only this specific disk which causes problems. I have tried on 3 different computers with the same result. A hint to the problem may be that if I add the disk to a windows system(With usb) the disk is called "A fixed disk" and not a portable disk as expected. The disk works fine with linux If i connect it with the sata cabel, but I would really like to have it working with usb too. (To mount it on computers without sata). Added: I did try to mount /dev/sg3 but mount say that its not a block device. (File say Its a character special device). Added output from dmesg: [ 97.454073] usb 7-1: USB disconnect, address 2 [ 105.913055] hub 2-0:1.0: unable to enumerate USB device on port 3 [ 107.048054] usb 2-3: new high speed USB device using ehci_hcd and address 5 [ 107.162900] usb 2-3: New USB device found, idVendor=1b1c, idProduct=1ab8 [ 107.162903] usb 2-3: New USB device strings: Mfr=1, Product=2, SerialNumber=5 [ 107.162906] usb 2-3: Product: CSSD-R60GB2 [ 107.162908] usb 2-3: Manufacturer: Corsair [ 107.162910] usb 2-3: SerialNumber: 10111441000000990069 [ 107.167651] scsi7 : usb-storage 2-3:1.0 [ 108.195543] scsi 7:0:0:0: Direct-Access Corsair CSSD-R60GB2 PQ: 1 ANSI: 0 [ 108.197732] scsi 7:0:0:0: Attached scsi generic sg3 type 0

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  • How should an experienced Windows SysAdmin learn Linux? [closed]

    - by Systemspoet
    I have a new hire starting in a few weeks who is an experienced Windows SysAdmin. I think he's fairly senior on the Windows side, with a pretty deep AD understanding and experience with Exchange 2007, 2010, and exchange migrations. He's done a little PowerShell but I suspect more of the "run this command to do this" variety then "write a script to do this" sort. However, we are a mixed shop and (he knows this) I expect him to become a reasonably competent Linux SysAdmin over time. I'm looking for good starting points to bring him along. I have over ten years of Linux/UNIX experience, so it all sort of seems intuitive to me, but I've been thinking about the toolkit you actually need to be productive in the Linux CLI world. Just to be able to use the machines at all, off the top of my head... vi Basic CLI stuff -- move around, rename files, copy files, tar, gzip, changing passwords, finding relevant manpages, keep track of where you are, find things in your history, etc, etc. More advanced things that I take for granted but are actually pretty hard -- doing things with 'find', extracting relevant text via 'awk' and/or 'cut', knowing when to use 'grep' and when to use 'grep -e' or 'egrep'. Distribution specific stuff... compiling software, rpm, yum, apt-get, you name it. This all seems pretty basic to me, but when I think back to 1995 when I was first learning my way, some of those things took me years to master. So my question is -- where should I send him to pick up those skills? I'm not just thinking of classes, but rather also websites and books? Where do you all suggest as a starting point for picking up Linux skills?

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  • Getting timing consistency in Linux

    - by Jim Hunziker
    I can't seem to get a simple program (with lots of memory access) to achieve consistent timing in Linux. I'm using a 2.6 kernel, and the program is being run on a dual-core processor with realtime priority. I'm trying to disable cache effects by declaring the memory arrays as volatile. Below are the results and the program. What are some possible sources of the outliers? Results: Number of trials: 100 Range: 0.021732s to 0.085596s Average Time: 0.058094s Standard Deviation: 0.006944s Extreme Outliers (2 SDs away from mean): 7 Average Time, excluding extreme outliers: 0.059273s Program: #include <stdio.h> #include <stdlib.h> #include <math.h> #include <sched.h> #include <sys/time.h> #define NUM_POINTS 5000000 #define REPS 100 unsigned long long getTimestamp() { unsigned long long usecCount; struct timeval timeVal; gettimeofday(&timeVal, 0); usecCount = timeVal.tv_sec * (unsigned long long) 1000000; usecCount += timeVal.tv_usec; return (usecCount); } double convertTimestampToSecs(unsigned long long timestamp) { return (timestamp / (double) 1000000); } int main(int argc, char* argv[]) { unsigned long long start, stop; double times[REPS]; double sum = 0; double scale, avg, newavg, median; double stddev = 0; double maxval = -1.0, minval = 1000000.0; int i, j, freq, count; int outliers = 0; struct sched_param sparam; sched_getparam(getpid(), &sparam); sparam.sched_priority = sched_get_priority_max(SCHED_FIFO); sched_setscheduler(getpid(), SCHED_FIFO, &sparam); volatile float* data; volatile float* results; data = calloc(NUM_POINTS, sizeof(float)); results = calloc(NUM_POINTS, sizeof(float)); for (i = 0; i < REPS; ++i) { start = getTimestamp(); for (j = 0; j < NUM_POINTS; ++j) { results[j] = data[j]; } stop = getTimestamp(); times[i] = convertTimestampToSecs(stop-start); } free(data); free(results); for (i = 0; i < REPS; i++) { sum += times[i]; if (times[i] > maxval) maxval = times[i]; if (times[i] < minval) minval = times[i]; } avg = sum/REPS; for (i = 0; i < REPS; i++) stddev += (times[i] - avg)*(times[i] - avg); stddev /= REPS; stddev = sqrt(stddev); for (i = 0; i < REPS; i++) { if (times[i] > avg + 2*stddev || times[i] < avg - 2*stddev) { sum -= times[i]; outliers++; } } newavg = sum/(REPS-outliers); printf("Number of trials: %d\n", REPS); printf("Range: %fs to %fs\n", minval, maxval); printf("Average Time: %fs\n", avg); printf("Standard Deviation: %fs\n", stddev); printf("Extreme Outliers (2 SDs away from mean): %d\n", outliers); printf("Average Time, excluding extreme outliers: %fs\n", newavg); return 0; }

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  • Throwing a C++ exception from inside a Linux Signal handler

    - by SoapBox
    As a thought experiment more than anything I am trying to get a C++ exception thrown "from" a linux signal handler for SIGSEGV. (I'm aware this is not a solution to any real world SIGSEGV and should never actually be done, but I thought I would try it out after being asked about it, and now I can't get it out of my head until I figure out how to do it.) Below is the closest I have come, but instead of the signal being caught properly, terminate() is being called as if no try/catch block is available. Anyone know why? Or know a way I can actually get a C++ exception from a signal handler? The code (beware, the self modifying asm limits this to running on x86_64 if you're trying to test it): #include <iostream> #include <stdexcept> #include <signal.h> #include <stdint.h> #include <errno.h> #include <string.h> #include <sys/mman.h> using namespace std; uint64_t oldaddr = 0; void thrower() { cout << "Inside thrower" << endl; throw std::runtime_error("SIGSEGV"); } void segv_handler(int sig, siginfo_t *info, void *pctx) { ucontext_t *context = (ucontext_t *)pctx; cout << "Inside SIGSEGV handler" << endl; oldaddr = context->uc_mcontext.gregs[REG_RIP]; uint32_t pageSize = (uint32_t)sysconf(_SC_PAGESIZE); uint64_t bottomOfOldPage = (oldaddr/pageSize) * pageSize; mprotect((void*)bottomOfOldPage, pageSize*2, PROT_READ|PROT_WRITE|PROT_EXEC); // 48 B8 xx xx xx xx xx xx xx xx = mov rax, xxxx *((uint8_t*)(oldaddr+0)) = 0x48; *((uint8_t*)(oldaddr+1)) = 0xB8; *((int64_t*)(oldaddr+2)) = (int64_t)thrower; // FF E0 = jmp rax *((uint8_t*)(oldaddr+10)) = 0xFF; *((uint8_t*)(oldaddr+11)) = 0xE0; } void func() { try { *(uint32_t*)0x1234 = 123456789; } catch (...) { cout << "caught inside func" << endl; throw; } } int main() { cout << "Top of main" << endl; struct sigaction action, old_action; action.sa_sigaction = segv_handler; sigemptyset(&action.sa_mask); action.sa_flags = SA_SIGINFO | SA_RESTART | SA_NODEFER; if (sigaction(SIGSEGV, &action, &old_action)<0) cerr << "Error setting handler : " << strerror(errno) << endl; try { func(); } catch (std::exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The actual output: Top of main Inside SIGSEGV handler Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): SIGSEGV Aborted Expected output: Top of main Inside thrower caught inside func Caught : SIGSEGV Bottom of main

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  • Binary data from a serial port in linux using c

    - by user1680393
    I am reading binary data from a serial port on Phidget sbc using Linux to get a command from an application running on a PC. I wrote a test program in VB to read the data into a byte array and convert it to decimal to use it but can’t figure out how to do it in c. I am unable to come up with anything with the research I have done on the internet. Command sent from PC is 0x0F. To check if I am getting correct data I read the data and send it back. Here is what I get back. Returned data has a carriage return added to it. Hex Display 0F00 0000 0D ‘\’ Display \0F\00\00\00\r Normal display just display a strange character. This tells me that the data is there that I can use, but can’t figure out to extract the value 0F or 15. How can I convert the incoming data to use it? I tried converting the received data using strtol, but it returns 0. I also tried setting the port to raw but it did not make any difference. unsigned char buffer1[1]; int ReadPort1() { int result; result = read(file1, &buffer1,1); if(result > 0) { WritePort1(buffer1); sprintf(tempstr, "Port1 data %s %d", buffer1, result); DisplayText(2,tempstr); } return result; } Port Open/Setup void OpenPort1() { //file1 = open("/dev/ttyUSB1", O_RDWR | O_NOCTTY | O_NONBLOCK); file1 = open("/dev/ttyUSB1", O_RDWR | O_NOCTTY | O_NODELAY); if(file1 < 0) printf("Error opening serial port1.\n"); else { SetPort(file1, 115200, 8, 1, 0, 1); port1open = 1; } } void SetPort(int fd, int Baud_Rate, int Data_Bits, int Stop_Bits, int Parity, int raw) { long BAUD; // derived baud rate from command line long DATABITS; long STOPBITS; long PARITYON; long PARITY; struct termios newtio; switch (Baud_Rate) { case 115200: BAUD = B115200; break; case 38400: BAUD = B38400; break; case 19200: BAUD = B19200; break; case 9600: BAUD = B9600; break; } //end of switch baud_rate switch (Data_Bits) { case 8: default: DATABITS = CS8; break; case 7: DATABITS = CS7; break; case 6: DATABITS = CS6; break; case 5: DATABITS = CS5; break; } //end of switch data_bits switch (Stop_Bits) { case 1: default: STOPBITS = 0; break; case 2: STOPBITS = CSTOPB; break; } //end of switch stop bits switch (Parity) { case 0: default: //none PARITYON = 0; PARITY = 0; break; case 1: //odd PARITYON = PARENB; PARITY = PARODD; break; case 2: //even PARITYON = PARENB; PARITY = 0; break; } //end of switch parity newtio.c_cflag = BAUD | DATABITS | STOPBITS | PARITYON | PARITY | CLOCAL | CREAD; newtio.c_iflag = IGNPAR; if(raw == 1) { newtio.c_oflag &= ~OPOST; newtio.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); } else { newtio.c_lflag = 0; //ICANON; newtio.c_oflag = 0; } newtio.c_cc[VMIN]=1; newtio.c_cc[VTIME]=0; tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&newtio); }

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  • Help with simple linux shell implementation

    - by nunos
    I am implementing a simple version of a linux shell in c. I have succesfully written the parser, but I am having some trouble forking out the child process. However, I think the problem is due to arrays, pointers and such, because just started C with this project and am not still very knowledgable with them. I am getting a segmentation fault and don't know where from. Any help is greatly appreciated. #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <sys/wait.h> #include <sys/types.h> #define MAX_COMMAND_LENGTH 250 #define MAX_ARG_LENGTH 250 typedef enum {false, true} bool; typedef struct { char **arg; char *infile; char *outfile; int background; } Command_Info; int parse_cmd(char *cmd_line, Command_Info *cmd_info) { char *arg; char *args[MAX_ARG_LENGTH]; int i = 0; arg = strtok(cmd_line, " "); while (arg != NULL) { args[i] = arg; arg = strtok(NULL, " "); i++; } int num_elems = i; if (num_elems == 0) return -1; cmd_info->infile = NULL; cmd_info->outfile = NULL; cmd_info->background = 0; int iarg = 0; for (i = 0; i < num_elems-1; i++) { if (!strcmp(args[i], "<")) { if (args[i+1] != NULL) cmd_info->infile = args[++i]; else return -1; } else if (!strcmp(args[i], ">")) { if (args[i+1] != NULL) cmd_info->outfile = args[++i]; else return -1; } else cmd_info->arg[iarg++] = args[i]; } if (!strcmp(args[i], "&")) cmd_info->background = true; else cmd_info->arg[iarg++] = args[i]; cmd_info->arg[iarg] = NULL; return 0; } void print_cmd(Command_Info *cmd_info) { int i; for (i = 0; cmd_info->arg[i] != NULL; i++) printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]); printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]); printf("infile=\"%s\"\n", cmd_info->infile); printf("outfile=\"%s\"\n", cmd_info->outfile); printf("background=\"%d\"\n", cmd_info->background); } void get_cmd(char* str) { fgets(str, MAX_COMMAND_LENGTH, stdin); str[strlen(str)-1] = '\0'; //apaga o '\n' do fim } pid_t exec_simple(Command_Info *cmd_info) { pid_t pid = fork(); if (pid < 0) { perror("Fork Error"); return -1; } if (pid == 0) { execvp(cmd_info->arg[0], cmd_info->arg); perror(cmd_info->arg[0]); exit(1); } return pid; } int main(int argc, char* argv[]) { while (true) { char cmd_line[MAX_COMMAND_LENGTH]; Command_Info cmd_info; printf(">>> "); get_cmd(cmd_line); if ( (parse_cmd(cmd_line, &cmd_info) == -1) ) return -1; parse_cmd(cmd_line, &cmd_info); if (!strcmp(cmd_info.arg[0], "exit")) exit(0); pid_t pid = exec_simple(&cmd_info); waitpid(pid, NULL, 0); } return 0; } Thanks.

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  • Problems with blocking reads using libudev on Linux

    - by Steve Hawkins
    We are using the following routine (on Linux, with libudev) to read data from a PIC microcontroller configured as a USB HID device. The data is sent only when a button connected to the PIC microcontroller is pressed or released. The routine is missing messages from the PIC controller, and I suspect that this is because the call to poll below is not behaving as it should. The call to poll will reliably block for 1 second util the first message is read. As soon as the first message is read, the call to poll returns immediately instead of blocking for 1 second (1000 milliseconds) like it should. I have worked around this problem by closing and re-opening the device after each read. This makes poll behave correctly, but I think that closing and re-opening the device may be the reason for the lost messages. bool PicIo::Receive (unsigned char* picData, const size_t picDataSize) { static hiddev_report_info hidReportInfo; static hiddev_usage_ref_multi hidUsageRef; if (-1 == PicDeviceDescriptor()) { return false; } // Determine whether or not there is data available to be read pollfd pollFd; pollFd.fd = PicDeviceDescriptor(); pollFd.events = POLLIN; int dataPending = poll (&pollFd, 1, 1000); if (dataPending <= 0) { return false; } // Initialize the HID Report structure for an input report hidReportInfo.report_type = HID_REPORT_TYPE_INPUT; hidReportInfo.report_id = 0; hidReportInfo.num_fields = 64; if (-1 == ioctl(PicDeviceDescriptor(), HIDIOCGREPORT, &hidReportInfo)) { return false; } // Initizlize the HID Usage Reference for an Input report hidUsageRef.uref.report_type = HID_REPORT_TYPE_INPUT; hidUsageRef.uref.report_id = 0; hidUsageRef.uref.field_index = 0; hidUsageRef.uref.usage_index = 0; hidUsageRef.num_values = 64; if (-1 == ioctl(PicDeviceDescriptor(), HIDIOCGUSAGES, &hidUsageRef)) { return false; } // Transfer bytes from the usage report into the return value. for (size_t idx=0; (idx < 64) && (idx < picDataSize); ++idx) { picData[idx] = hidUsageRef.values[idx]; } return true; } The function PicDeviceDescriptor() does checking on the device to make sure that it is present. Here are the pertinent details of the PicDeviceDescriptor function, showing how the device is begin opened. int PicIo::PicDeviceDescriptor(int command) { struct stat statInfo; static int picDeviceDescriptor = -1; string picDevicePath = "/dev/usb/hiddev0"; if ((-1 != picDeviceDescriptor) && (CLOSE == command)) { close (picDeviceDescriptor); picDeviceDescriptor = -1; } else if ((-1 != picDeviceDescriptor) && (-1 == fstat(picDeviceDescriptor, &statInfo))) { // Handle the case where the PIC device had previously been detected, and // is now disconnected. close (picDeviceDescriptor); picDeviceDescriptor = -1; } else if ((-1 == picDeviceDescriptor) && (m_picDevice.IsConnected())) { // Create the PIC device descriptor if the PIC device is present (i.e. its // device node is present) and if the descriptor does not already exist picDeviceDescriptor = open (picDevicePath.c_str(), O_RDONLY); } return picDeviceDescriptor; } I'm sure that I'm doing something wrong, but I've Googled the issue and cannot seem to find any relevant answers. Any help would be very much appreciated -- Thx.

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  • Spring ResourceServlet throws too many open files exception in jetty and tomcat under linux

    - by atomsfat
    I was running the petclinic example that was created with spring roo, also I test booking-mvc example that comes whit spring webflow 2.0.9 and the same happens, this is when I reload the main page many times. If I remove the lines from both examples there is no error. < spring:theme code="styleSheet" var="theme_css"/> <spring:url value="/${theme_css}" var="theme_css_url"/> <spring:url value="/resources/dojo/dojo.js" var="dojo_url"/> <spring:url value="/resources/dijit/themes/tundra/tundra.css" var="tundra_url"/> <spring:url value="/resources/spring/Spring.js" var="spring_url"/> <spring:url value="/resources/spring/Spring-Dojo.js" var="spring_dojo_url"/> <spring:url value="/static/images/favicon.ico" var="favicon" /> <link rel="stylesheet" type="text/css" media="screen" href="${theme_css_url}"><!-- //required for FF3 and Opera --></link> <link rel="stylesheet" type="text/css" href="${tundra_url}"><!-- //required for FF3 and Opera --></link> <link rel="SHORTCUT ICON" href="${favicon}" /> <script src="${dojo_url}" type="text/javascript" ><!-- //required for FF3 and Opera --></script> <script src="${spring_url}" type="text/javascript"><!-- //required for FF3 and Opera --></script> <script src="${spring_dojo_url}" type="text/javascript"><!-- //required for FF3 and Opera --></script> <script language="JavaScript" type="text/javascript">dojo.require("dojo.parser");</script> So I can deduce that this is something related with this servlet <servlet> <servlet-name>Resource Servlet</servlet-name> <servlet-class>org.springframework.js.resource.ResourceServlet</servlet-class> </servlet> <!-- Map all /resources requests to the Resource Servlet for handling --> <servlet-mapping> <servlet-name>Resource Servlet</servlet-name> <url-pattern>/resources/*</url-pattern> </servlet-mapping> Running the example injetty 6.1.10, tomcat 1.6, in fedora 12 with java 1.6.20, make errors. but in aix and websphere no errors, and tomcat 1.6 and windows no errors, I think that this is something related with linux. STACKTRACE 2010-05-21 12:53:07.733::WARN: Nested in org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.apache.tiles.impl.CannotRenderException: ServletException including path '/WEB-INF/layouts/default.jspx'.: org.apache.tiles.impl.CannotRenderException: ServletException including path '/WEB-INF/layouts/default.jspx'. at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:691) at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:643) at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:626) at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:322) at org.springframework.web.servlet.view.tiles2.TilesView.renderMergedOutputModel(TilesView.java:100) at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250) at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1060) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:798) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:716) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:647) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:552) at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:726) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:285) at org.mortbay.jetty.servlet.Dispatcher.error(Dispatcher.java:135) at org.mortbay.jetty.servlet.ErrorPageErrorHandler.handle(ErrorPageErrorHandler.java:121) at org.mortbay.jetty.Response.sendError(Response.java:274) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:429) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:726) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:206) at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) at org.mortbay.jetty.Server.handle(Server.java:324) at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505) at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:829) at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:514) at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211) at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380) at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395) at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488) Caused by: org.apache.tiles.util.TilesIOException: ServletException including path '/WEB-INF/layouts/default.jspx'. at org.apache.tiles.servlet.context.ServletUtil.wrapServletException(ServletUtil.java:232) at org.apache.tiles.servlet.context.ServletTilesRequestContext.forward(ServletTilesRequestContext.java:243) at org.apache.tiles.servlet.context.ServletTilesRequestContext.dispatch(ServletTilesRequestContext.java:222) at org.apache.tiles.renderer.impl.TemplateAttributeRenderer.write(TemplateAttributeRenderer.java:44) at org.apache.tiles.renderer.impl.AbstractBaseAttributeRenderer.render(AbstractBaseAttributeRenderer.java:103) at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:669) at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:689) ... 38 more Caused by: java.io.FileNotFoundException: /home/tsalazar/Workspace/test/roo_clinic/src/main/webapp/WEB-INF/web.xml (Too many open files) at java.io.FileInputStream.open(Native Method) at java.io.FileInputStream.<init>(FileInputStream.java:106) at java.io.FileInputStream.<init>(FileInputStream.java:66) at sun.net.www.protocol.file.FileURLConnection.connect(FileURLConnection.java:70) at sun.net.www.protocol.file.FileURLConnection.getInputStream(FileURLConnection.java:161) at java.net.URL.openStream(URL.java:1010) at org.apache.jasper.compiler.JspConfig.processWebDotXml(JspConfig.java:114) at org.apache.jasper.compiler.JspConfig.init(JspConfig.java:295) at org.apache.jasper.compiler.JspConfig.findJspProperty(JspConfig.java:360) at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:141) at org.apache.jasper.compiler.Compiler.compile(Compiler.java:409) at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:592) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:344) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:470) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:364) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:726) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:285) at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:126) at org.apache.tiles.servlet.context.ServletTilesRequestContext.forward(ServletTilesRequestContext.java:241) ... 43 more

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