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  • Synchronization between user space process and interupt context code

    - by user1748950
    Recently I attended couple of interviews. Out of all kernel questions which were asked, thr is one specific question which I couldnt find convincing answer of. How will you use different synchronization techniques while sharing data between user space process and interrupt context function? My convincing answer was: In interrupt context code: 1. do *spin_lock_irqsave* 2. access data buffer which is shared between user space app and kernel 3. do *spin_lock_irqrestore* Then this was not convincing answer. Do I have to do irqsave and irqrestore in all the instances of data access? Regards, Yogi

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  • Why thread specific data is required in pthread ?

    - by user504542
    Hi As i know, all the threads share memory location. For example a global variable changes in one thread will reflect in another thread. Since each thread has its own stack, the local variables that are created inside the thread is unique. In this case, why do we need to go for thread specific data mechanism?. Can't it be achieved by auto storage varibles inside the thread function ? Kindly clarify!!!. BR Rj

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  • Use sudo su - <username> to access the <username's> account but sudo su - shouldn't be possible with a sudo user

    - by Winnie
    There is a requirement I got. My sudo users (for which their entry in sudoers file) should be able to access other user's account say Oracle using following command: sudo su - Oracle The above should work with giving current users password. But if the same user is firing the following command, sudo su - it shouldn't work and thus root access shouldnt be given to current user. I am not using su because because i dont want current user to know the credentials of other user(root,Oracle etc.). Can anyone please help me . Its urgent...

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  • How to determinate file in Perl

    - by rodnower
    Hello, I use File::Find - find(\&f, $directory) for find some file with some content. Relevant part of my delegate looks like: sub f { my $file = $File::Find::name; return unless -f $file; return unless $file =~ /$file_pattern/; etc... but the problem is that, that this code returns every time where $file not exist in current directory. For example for file ./test it fine, but for file ./dir/test this return... Is there some better way to know if $file is file?

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  • How to fill a structure when a pointer to it, is passed as an argument to a function

    - by Ram
    I have a function: func (struct passwd* pw) { struct passwd* temp; struct passwd* save; temp = getpwnam("someuser"); /* since getpwnam returns a pointer to a static * data buffer, I am copying the returned struct * to a local struct. */ if(temp) { save = malloc(sizeof *save); if (save) { memcpy(save, temp, sizeof(struct passwd)); /* Here, I have to update passed pw* with this save struct. */ *pw = *save; /* (~ memcpy) */ } } } The function which calls func(pw) is able to get the updated information. But is it fine to use it as above. The statement *pw = *save is not a deep copy. I do not want to copy each and every member of structure one by one like pw-pw_shell = strdup(save-pw_shell) etc. Is there any better way to do it? Thanks.

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  • Is this time related process accounting stats gathering appropriate?

    - by Ceko Cakata
    Based on sys/acct.h (V1, not V3) I need to gather some user usage statistics based on a parser that parser the acct file line by line. The parser will run and parse the entire file every N seconds and I need to gather user statistics accumulated since the last run (N seconds back). I'm not sure what will be the most appropriate way to do it based on the info provided by sys/acct.h. Maybe something like this: if ((ac_btime + ac_etime) < (current_time - N)) { gather; } Also comp_t is said to be "floating-point value consisting of a 3-bit, base-8 exponent, and a 13-bit mantissa", but I think u_int16_t is just a unsigned short int. Should I be converting it to long it with the provided formula or not?

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  • find string from the file in somewhere

    - by lightmanhk
    I want to find a string from some file in subdirectory. Like we are in bundle/. and in bundle/ there are multiple subdirectories and multiple txt files I want to do something like find . -type f -exec grep "\<F8\>" {} \; want to get the file where it contain string < F8 this command does work, find the string, but never return filename I hope anyone can give me a better solution to this, like display filename along with the line containing that string

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  • sed: group capturing

    - by Michael
    Is there any way to tell sed to output only captured groups? for example given by input: This is a sample 123 text and some 987 numbers and pattern /([\d]+)/ I could get only 123 and 987 output in the way formatted by back references perhaps?

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  • Testing shared memory ,strange thing happen

    - by barfatchen
    I have 2 program compiled in 4.1.2 running in RedHat 5.5 , It is a simple job to test shared memory , shmem1.c like following : #define STATE_FILE "/program.shared" #define NAMESIZE 1024 #define MAXNAMES 100 typedef struct { char name[MAXNAMES][NAMESIZE]; int heartbeat ; int iFlag ; } SHARED_VAR; int main (void) { int first = 0; int shm_fd; static SHARED_VAR *conf; if((shm_fd = shm_open(STATE_FILE, (O_CREAT | O_EXCL | O_RDWR), (S_IREAD | S_IWRITE))) > 0 ) { first = 1; /* We are the first instance */ } else if((shm_fd = shm_open(STATE_FILE, (O_CREAT | O_RDWR), (S_IREAD | S_IWRITE))) < 0) { printf("Could not create shm object. %s\n", strerror(errno)); return errno; } if((conf = mmap(0, sizeof(SHARED_VAR), (PROT_READ | PROT_WRITE), MAP_SHARED, shm_fd, 0)) == MAP_FAILED) { return errno; } if(first) { for(idx=0;idx< 1000000000;idx++) { conf->heartbeat = conf->heartbeat + 1 ; } } printf("conf->heartbeat=(%d)\n",conf->heartbeat) ; close(shm_fd); shm_unlink(STATE_FILE); exit(0); }//main And shmem2.c like following : #define STATE_FILE "/program.shared" #define NAMESIZE 1024 #define MAXNAMES 100 typedef struct { char name[MAXNAMES][NAMESIZE]; int heartbeat ; int iFlag ; } SHARED_VAR; int main (void) { int first = 0; int shm_fd; static SHARED_VAR *conf; if((shm_fd = shm_open(STATE_FILE, (O_RDWR), (S_IREAD | S_IWRITE))) < 0) { printf("Could not create shm object. %s\n", strerror(errno)); return errno; } ftruncate(shm_fd, sizeof(SHARED_VAR)); if((conf = mmap(0, sizeof(SHARED_VAR), (PROT_READ | PROT_WRITE), MAP_SHARED, shm_fd, 0)) == MAP_FAILED) { return errno; } int idx ; for(idx=0;idx< 1000000000;idx++) { conf->heartbeat = conf->heartbeat + 1 ; } printf("conf->heartbeat=(%d)\n",conf->heartbeat) ; close(shm_fd); exit(0); } After compiled : gcc shmem1.c -lpthread -lrt -o shmem1.exe gcc shmem2.c -lpthread -lrt -o shmem2.exe And Run both program almost at the same time with 2 terminal : [test]$ ./shmem1.exe First creation of the shm. Setting up default values conf->heartbeat=(840825951) [test]$ ./shmem2.exe conf->heartbeat=(1215083817) I feel confused !! since shmem1.c is a loop 1,000,000,000 times , how can it be possible to have a answer like 840,825,951 ? I run shmem1.exe and shmem2.exe this way,most of the results are conf-heartbeat will larger than 1,000,000,000 , but seldom and randomly , I will see result conf-heartbeat will lesser than 1,000,000,000 , either in shmem1.exe or shmem2.exe !! if run shmem1.exe only , it is always print 1,000,000,000 , my question is , what is the reason cause conf-heartbeat=(840825951) in shmem1.exe ? Update: Although not sure , but I think I figure it out what is going on , If shmem1.exe run 10 times for example , then conf-heartbeat = 10 , in this time shmem1.exe take a rest and then back , shmem1.exe read from shared memory and conf-heartbeat = 8 , so shmem1.exe will continue from 8 , why conf-heartbeat = 8 ? I think it is because shmem2.exe update the shared memory data to 8 , shmem1.exe did not write 10 back to shared memory before it took a rest ....that is just my theory... i don't know how to prove it !!

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  • Why fork() before setsid()

    - by corentin.kerisit
    Why fork() before setsid() to daemonize a process ? Basically, if I want to detach a process from its controlling terminal and make it a process group leader : I use setsid(). Doing this without forking before doesn't work. Why ? Thanks :)

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  • Is it possible to wrap calls to statically linked 3rd party library?

    - by robusta
    Hi, I would like to trace calls to some 3rd party library which are made from another 3rd party library. Example: I want to trace calls to library A. My application statically links library B, which in turn is statically linked to library A. In case of dynamic linking I could write library A2 with wrappers for functions which I want to trace of library A and use LD_PRELOAD=A2.so. Then, my wrappers will be called instead, and I will see the trace. In my case I cannot use dynamic linking. Is it possible to achieve the same using static linking? Thanks, Robusta

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  • Ubuntu 10.10, taskbar

    - by Alex
    I launched system monitor to kill one program, which didn't responded on any mouse clicks, etc. But i occasionally killed another process. so, taskbar was killed. (it was in the bottom of the screen, in the top all is good) reboot didnt help o_O. Now I use Alt-Tab and alt-controll-arrows to switch between programs and desktops (it works). How to launch taskbar again? its very strange that reboot didnt help me.

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  • How do I write a bash script to replace words in files and then rename files?

    - by Jason
    Hi All, I have a folder structure, as shown below: I need to create a bash script that does 4 things: It searches all the files in the generic directory and finds the string 'generic' and makes it into 'something' As above, but changes "GENERIC" to "SOMETHING" As above, but changes "Generic" to "Something" Renames any filename that has "generic" in it with "something" Right now I am doing this process manually by using the search and replace in net beans. I dont know much about bash scripting, but i'm sure this can be done. I'm thinking of something that I would run and it would take "Something" as the input. Where would I start? what functions should I use? overall guidance would be great. thanks. I am using Ubuntu 10.5 desktop edition.

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  • Getting rails to execute root level file edits on system files without compromising security.

    - by voxobscuro
    I'm writing a Rails 3 application that needs to be able to trigger modifications to unix system config files. I'd like to insulate the file modifications from the consumer side by running them in a background process. I've considered writing out a temp file in rails and then copying the file with a bash script but that doesn't really insulate the system. I've also considered pulling from the database manually with a cron based script and updating the configs. But what I would really like is a component that can hook into the rails environment, read out what is needed from the database, and update the config files. This process needs to be run as root because the config files mostly live in /etc/whatever. Any suggestions? Thanks!

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  • remove the content in directory and subdirectory hierarichally with out distroy the directory structure

    - by user3713876
    In shell script, I want to clear only text files and log files in the following structure with out removing the directory as well as subdirectories | |------bar/ | |---file1.txt |---file2.txt | |---subdir1/ | |---file1.log | |---file2.log | |---subdir2/ |---image1.log |---image2.log I am using rm -rf /bar/* so I am getting the result as follows. |------bar/ but I want the output like following | |------bar/ | | | | |---subdir1/ | | | |---subdir2/ I want to remove only text files or log files or csv with out removing the directory and the subdirectories

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  • How to make shell output redirect (>) write while script is still running?

    - by Noio
    I wrote a short script that never terminates. This script continuously generates output that I have to check on every now and then. I'm running it on a lab computer through SSH, and redirecting the output to a file in my public_html folder on that machine. python script.py > ~/public_html/results.txt However, the results don't show up immediately when I refresh the address. The results show up when I terminate the program, but as I said, it doesn't halt by itself. Is that redirect (>) being lazy with with writing? Is there a way to continuously (or with an interval) update the results in the file? Or is it the webserver that doesn't update the file while it is still being written?

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