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Search found 333 results on 14 pages for 'posix'.

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  • monitoring unix resources from inside a process

    - by kamziro
    I've had a bunch of EAGAIN's from trying to fork() or spawning threads, which lead me to believe that I'm leaking resources somewhere. Is it possible, in POSIX, to get the following from inside the process itself: number of active pthreads number of active child processes number of active pipes number of active sockets (or maybe this and pipes would be counted as file descriptors?) Or do these have to be counted manually? There's already counters for them, but I think one of them are leaking.

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  • what if _POSIX_VDISABLE value is -1?

    - by Nagaraj
    In POSIX _POSIX_VDISABLE value if -1, there is no disabling character for special character for all the terminal device files; otherwise the value is the disabling character value.. Can please anyone help me understand this. I m not able to get the exact meaning of this. Please

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  • Permissions issue Mac OS X Client -> Mac OS X Server

    - by Meltemi
    I can't get access to a folder on our server and can't understand why. Perhaps someone will see what I'm overlooking... Trouble accessing /Library/Subdirectory/NextDirectory/ User joe can ssh to the server just fine and cd to /Library/Subdirectory/ however trying to cd into the next folder, NextDirectory, gives this error: -bash: cd: NextDirectory/: Permission denied both username joe & bill are members of the group admin and both can get INTO Subdirectory without any trouble... hostname:Library joe$ ls -l | grep Subdirectory drwxrwxr-x 3 bill admin 102 Jun 1 14:51 Subdirectory and from w/in the Subversion folder hostname:Subdirectory joe$ ls -l drwxrwx--- 5 root admin 170 Jun 1 22:19 NextDirectory bill can cd into NextDirectory but joe cannot!?! What am I overlooking? What tools do we have to troubleshoot this? thanks!

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  • Monitoring and terminating a hanged process in Linux

    - by Yoav
    Hi, I'm writing a script that runs many simultaneous processes that run the "dig" command. Once in a while (relatively rare, but happens in every run since I run dig many times) the dig command hangs with 0% CPU. Therefore, my script never terminates. I've created a monitor process for each dig command I run, which terminates it after a while, but I was wondering if there isn't a simpler and more efficient way to run a process with a pre-determined "expiration date", i.e. if the process runs more then X seconds it gets a signal that terminates it. Thanks!

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  • Mutt and msmtp interoperability

    - by illusionoflife
    I am working on configuring /mutt/ to send mail via /msmtp/. Strangely, if I user /msmtp/ from shell, all okay, that means, that .msmtprc is correct. However, mail sent with mutt do not come. I have this line in .muttrc. set sendmail="msmtp" How can I debug this problem? EDIT: I found, that if I send just text, like msmtp 'my-email' <<< "Hello", it works. But if I send fully builded email-header, it do not. Is it gmail politics or what?

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  • Why is NTFS case sensitive?

    - by Luke
    I personally thought that NTFS was case insensitive, since you can type cmd, CMD, cMd or even CmD and still get the command prompt. However, why is it that during a CHKDSK x: /f /r, sometimes it fixes capitalization in some files? If it didn't care about the case, it shouldn't matter about that, and CHKDSK shouldn't be checking if it's actually CMD or cmd. Am I right? Where does it actually matter in the file system?

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  • bash pipe construct to prepend something to the stdoutput of previous command

    - by AndreasT
    I want to use sendmail to send me stuff and want to do it in a oneliner. echo "mail content" | sendmail emailataddres.com Sends it without subject. The subject line must come before the Mail content, so I am looking for something along the lines of: echo "mail content" | prepend "Subject: All that matters" | sendmail emailataddres.com sed and awk tend to be really awkward to use and remember. EDIT:Just to clarify: echo "Mail content" is just an illustrating example. I need to be able to prepend stuff to stdout streams from any source. e.g.: ifconfig, zcat, etc..

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  • Alternative to the tee command whitout STDOUT

    - by aef
    I'm using | sudo tee FILENAME to be able to write or append to a file for which superuser permissions are required quite often. Although I understand why it is helpful in some situation, that tee also sends its input to STDOUT again, I never ever actually used that part of tee for anything useful. In most situations, this feature only causes my screen to be filled with unwanted jitter, if I don't go the extra step and manually silence it with tee 1> /dev/null. My question: Is there is a command arround, which does exactly the same thing as tee, but does by default not output anything to STDOUT?

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  • Setting per-directory umask using ACLs

    - by Yarin
    We want to mimic the behavior of a system-wide 002 umask on a certain directory foo, in order to ensure the following result: All sub-directories created underneath foo will have 775 permissions All files created underneath foo and subdirectories will have 664 permissions 1 and 2 will happen for files/dirs created by all users, including root, and all daemons. Assuming that ACL is enabled on our partition, this is the command we've come up with: setfacl -R -d -m mask:002 foo This seems to be working- I'm basically just looking for confirmation. Is this the most effective way to apply a per-directory umask with an ACL?

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  • In C, how do you capture a group with regex?

    - by Sylvain
    Hi, I'm trying to extract a string from another using regex. I'm using the POSIX regex functions (regcomp, regexec ...), and I fail at capturing a group ... For instance, let the pattern be something as simple as "MAIL FROM:<(.*)>" (with REG_EXTENDED cflags) I want to capture everything between '<' and '' My problem is that regmatch_t gives me the boundaries of the whole pattern (MAIL FROM:<...) instead of just what's between the parenthesis ... What am I missing ? Thanks in advance,

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  • Using pthread condition variable with rwlock

    - by Doomsday
    Hello, I'm looking for a way to use pthread rwlock structure with conditions routines in C++. I have two questions: First: How is it possible and if we can't, why ? Second: Why current POSIX pthread have not implemented this behaviour ? To understand my purpose, I explain what will be my use: I've a producer-consumer model dealing with one shared array. The consumer will cond_wait when the array is empty, but rdlock when reading some elems. The producer will wrlock when adding(+signal) or removing elems from the array. The benefit of using rdlock instead of mutex_lock is to improve performance: when using mutex_lock, several readers would block, whereas using rdlock several readers would not block.

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  • Why does this Bash regex match return an Exit Status of "2"?

    - by PreservedMoose
    I'm writing a Bash script that needs to scan for the existence of non-ASCII characters in filenames. I'm using the POSIX bracket regex syntax to match the non-ASCII characters, but for some reason, when I test for the match in an if/then statement, the test always returns an Exit Status of 2, and never matches my test string. Here's the code in question: FILEREQ_SOURCEFILE="Filename–WithNonAScII-Charàcters-05sec_23.98.mov" REGEX_MATCH_NONASCII="[^[:ascii:]]" if [[ $FILEREQ_SOURCEFILE =~ $REGEX_MATCH_NONASCII ]]; then echo "Exit Status: $?" echo "Matched!" else echo "Exit Status: $?" echo "No Match" fi This code always returns: Exit Status: 2 No Match I've read and re-read the bash-hackers.org explanation of how regex matching works, as well as this previous question on SO regarding matching non-ASCII characters, but for the life of me, I can't get this to work. What am I missing here?

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  • How do you capture a group with regex?

    - by Sylvain
    Hi, I'm trying to extract a string from another using regex. I'm using the POSIX regex functions (regcomp, regexec ...), and I fail at capturing a group ... For instance, let the pattern be something as simple as "MAIL FROM:<(.*)>" (with REG_EXTENDED cflags) I want to capture everything between '<' and '' My problem is that regmatch_t gives me the boundaries of the whole pattern (MAIL FROM:<...) instead of just what's between the parenthesis ... What am I missing ? Thanks in advance, edit: some code #define SENDER_REGEX "MAIL FROM:<(.*)>" int main(int ac, char **av) { regex_t regex; int status; regmatch_t pmatch[1]; if (regcomp(&regex, SENDER_REGEX, REG_ICASE|REG_EXTENDED) != 0) printf("regcomp error\n"); status = regexec(&regex, av[1], 1, pmatch, 0); regfree(&regex); if (!status) printf( "matched from %d (%c) to %d (%c)\n" , pmatch[0].rm_so , av[1][pmatch[0].rm_so] , pmatch[0].rm_eo , av[1][pmatch[0].rm_eo] ); return (0); } outputs: $./a.out "012345MAIL FROM:<abcd>$" matched from 6 (M) to 22 ($) solution: as RarrRarrRarr said, the indices are indeed in pmatch[1].rm_so and pmatch[1].rm_eo hence regmatch_t pmatch[1]; becomes regmatch_t pmatch[2]; and regexec(&regex, av[1], 1, pmatch, 0); becomes regexec(&regex, av[1], 2, pmatch, 0); Thanks :)

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  • Serial: write() throttling?

    - by damian
    Hi everyone, I'm working on a project sending serial data to control animation of LED lights, which need to stay in sync with a sound engine. There seems to be a large serial write buffer (OSX (POSIX) + FTDI chipset usb serial device), so without manually restricting the transmission rate, the animation system can get several seconds ahead of the serial transmission. Currently I'm manually restricting the serial write speed to the baudrate (8N1 = 10 bytes serial frame per 8 bytes data, 19200 bps serial - 1920 bytes per second max), but I am having a problem with the sound drifting out of sync over time - it starts fine, but after 10 minutes there's a noticeable (100ms+) lag between the sound and the lights. This is the code that's restricting the serial write speed (called once per animation frame, 'elapsed' is the duration of the current frame, 'baudrate' is the bps (19200)): void BufferedSerial::update( float elapsed ) { baud_timer += elapsed; if ( bytes_written > 1024 ) { // maintain baudrate float time_should_have_taken = (float(bytes_written)*10)/float(baudrate); float time_actually_took = baud_timer; // sleep if we have > 20ms lag between serial transmit and our write calls if ( time_should_have_taken-time_actually_took > 0.02f ) { float sleep_time = time_should_have_taken - time_actually_took; int sleep_time_us = sleep_time*1000.0f*1000.0f; //printf("BufferedSerial::update sleeping %i ms\n", sleep_time_us/1000 ); delayUs( sleep_time_us ); // subtract 128 bytes bytes_written -= 128; // subtract the time it should have taken to write 128 bytes baud_timer -= (float(128)*10)/float(baudrate); } } } Clearly there's something wrong, somewhere. A much better approach would be to be able to determine the number of bytes currently in the transmit queue, and try and keep that below a fixed threshold. Any advice appreciated.

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  • How good is the memory mapped Circular Buffer on Wikipedia?

    - by abroun
    I'm trying to implement a circular buffer in C, and have come across this example on Wikipedia. It looks as if it would provide a really nice interface for anyone reading from the buffer, as reads which wrap around from the end to the beginning of the buffer are handled automatically. So all reads are contiguous. However, I'm a bit unsure about using it straight away as I don't really have much experience with memory mapping or virtual memory and I'm not sure that I fully understand what it's doing. What I think I understand is that it's mapping a shared memory file the size of the buffer into memory twice. Then, whenever data is written into the buffer it appears in memory in 2 places at once. This allows all reads to be contiguous. What would be really great is if someone with more experience of POSIX memory mapping could have a quick look at the code and tell me if the underlying mechanism used is really that efficient. Am I right in thinking for example that the file in /dev/shm used for the shared memory always stays in RAM or could it get written to the hard drive (performance hit) at some point? Are there any gotchas I should be aware of? As it stands, I'm probably going to use a simpler method for my current project, but it'd be good to understand this to have it in my toolbox for the future. Thanks in advance for your time.

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  • how to clear stack after stack overflow signal occur

    - by user353573
    In pthread, After reaching yellow zone in stack, signal handler stop the recursive function by making it return however, we can only continue to use extra area in yellow zone, how to clear the rubbish before the yellow zone in the thread stack ? (Copied from "answers"): #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <signal.h> #include <setjmp.h> #include <sys/mman.h> #include <unistd.h> #include <assert.h> #include <sys/resource.h> #define ALT_STACK_SIZE (64*1024) #define YELLOW_ZONE_PAGES (1) typedef struct { size_t stack_size; char* stack_pointer; char* red_zone_boundary; char* yellow_zone_boundary; sigjmp_buf return_point; size_t red_zone_size; } ThreadInfo; static pthread_key_t thread_info_key; static struct sigaction newAct, oldAct; bool gofromyellow = false; int call_times = 0; static void main_routine(){ // make it overflow if(gofromyellow == true) { printf("return from yellow zone, called %d times\n", call_times); return; } else { call_times = call_times + 1; main_routine(); gofromyellow = true; } } // red zone management static void stackoverflow_routine(){ fprintf(stderr, "stack overflow error.\n"); fflush(stderr); } // yellow zone management static void yellow_zone_hook(){ fprintf(stderr, "exceed yellow zone.\n"); fflush(stderr); } static int get_stack_info(void** stackaddr, size_t* stacksize){ int ret = -1; pthread_attr_t attr; pthread_attr_init(&attr); if(pthread_getattr_np(pthread_self(), &attr) == 0){ ret = pthread_attr_getstack(&attr, stackaddr, stacksize); } pthread_attr_destroy(&attr); return ret; } static int is_in_stack(const ThreadInfo* tinfo, char* pointer){ return (tinfo->stack_pointer <= pointer) && (pointer < tinfo->stack_pointer + tinfo->stack_size); } static int is_in_red_zone(const ThreadInfo* tinfo, char* pointer){ if(tinfo->red_zone_boundary){ return (tinfo->stack_pointer <= pointer) && (pointer < tinfo->red_zone_boundary); } } static int is_in_yellow_zone(const ThreadInfo* tinfo, char* pointer){ if(tinfo->yellow_zone_boundary){ return (tinfo->red_zone_boundary <= pointer) && (pointer < tinfo->yellow_zone_boundary); } } static void set_yellow_zone(ThreadInfo* tinfo){ int pagesize = sysconf(_SC_PAGE_SIZE); assert(pagesize > 0); tinfo->yellow_zone_boundary = tinfo->red_zone_boundary + pagesize * YELLOW_ZONE_PAGES; mprotect(tinfo->red_zone_boundary, pagesize * YELLOW_ZONE_PAGES, PROT_NONE); } static void reset_yellow_zone(ThreadInfo* tinfo){ size_t pagesize = tinfo->yellow_zone_boundary - tinfo->red_zone_boundary; if(mmap(tinfo->red_zone_boundary, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0) == 0){ perror("mmap failed"), exit(1); } mprotect(tinfo->red_zone_boundary, pagesize, PROT_READ | PROT_WRITE); tinfo->yellow_zone_boundary = 0; } static void signal_handler(int sig, siginfo_t* sig_info, void* sig_data){ if(sig == SIGSEGV){ ThreadInfo* tinfo = (ThreadInfo*) pthread_getspecific(thread_info_key); char* fault_address = (char*) sig_info->si_addr; if(is_in_stack(tinfo, fault_address)){ if(is_in_red_zone(tinfo, fault_address)){ siglongjmp(tinfo->return_point, 1); }else if(is_in_yellow_zone(tinfo, fault_address)){ reset_yellow_zone(tinfo); yellow_zone_hook(); gofromyellow = true; return; } else { //inside stack not related overflow SEGV happen } } } } static void register_application_info(){ pthread_key_create(&thread_info_key, NULL); sigemptyset(&newAct.sa_mask); sigaddset(&newAct.sa_mask, SIGSEGV); newAct.sa_sigaction = signal_handler; newAct.sa_flags = SA_SIGINFO | SA_RESTART | SA_ONSTACK; sigaction(SIGSEGV, &newAct, &oldAct); } static void register_thread_info(ThreadInfo* tinfo){ stack_t ss; pthread_setspecific(thread_info_key, tinfo); get_stack_info((void**)&tinfo->stack_pointer, &tinfo->stack_size); printf("stack size %d mb\n", tinfo->stack_size/1024/1024 ); tinfo->red_zone_boundary = tinfo->stack_pointer + tinfo->red_zone_size; set_yellow_zone(tinfo); ss.ss_sp = (char*)malloc(ALT_STACK_SIZE); ss.ss_size = ALT_STACK_SIZE; ss.ss_flags = 0; sigaltstack(&ss, NULL); } static void* thread_routine(void* p){ ThreadInfo* tinfo = (ThreadInfo*)p; register_thread_info(tinfo); if(sigsetjmp(tinfo->return_point, 1) == 0){ main_routine(); } else { stackoverflow_routine(); } free(tinfo); printf("after tinfo, end thread\n"); return 0; } int main(int argc, char** argv){ register_application_info(); if( argc == 2 ){ int stacksize = atoi(argv[1]); pthread_attr_t attr; pthread_attr_init(&attr); pthread_attr_setstacksize(&attr, 1024 * 1024 * stacksize); { pthread_t pid0; ThreadInfo* tinfo = (ThreadInfo*)calloc(1, sizeof(ThreadInfo)); pthread_attr_getguardsize(&attr, &tinfo->red_zone_size); pthread_create(&pid0, &attr, thread_routine, tinfo); pthread_join(pid0, NULL); } } else { printf("Usage: %s stacksize(mb)\n", argv[0]); } return 0; } C language in linux, ubuntu

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  • Thread scheduling Round Robin / scheduling dispatch

    - by MRP
    #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <semaphore.h> #define NUM_THREADS 4 #define COUNT_LIMIT 13 int done = 0; int count = 0; int quantum = 2; int thread_ids[4] = {0,1,2,3}; int thread_runtime[4] = {0,5,4,7}; pthread_mutex_t count_mutex; pthread_cond_t count_threshold_cv; void * inc_count(void * arg); static sem_t count_sem; int quit = 0; ///////// Inc_Count//////////////// void *inc_count(void *t) { long my_id = (long)t; int i; sem_wait(&count_sem); /////////////CRIT SECTION////////////////////////////////// printf("run_thread = %d\n",my_id); printf("%d \n",thread_runtime[my_id]); for( i=0; i < thread_runtime[my_id];i++) { printf("runtime= %d\n",thread_runtime[my_id]); pthread_mutex_lock(&count_mutex); count++; if (count == COUNT_LIMIT) { pthread_cond_signal(&count_threshold_cv); printf("inc_count(): thread %ld, count = %d Threshold reached.\n", my_id, count); } printf("inc_count(): thread %ld, count = %d, unlocking mutex\n",my_id, count); pthread_mutex_unlock(&count_mutex); sleep(1) ; }//End For sem_post(&count_sem); // Next Thread Enters Crit Section pthread_exit(NULL); } /////////// Count_Watch //////////////// void *watch_count(void *t) { long my_id = (long)t; printf("Starting watch_count(): thread %ld\n", my_id); pthread_mutex_lock(&count_mutex); if (count<COUNT_LIMIT) { pthread_cond_wait(&count_threshold_cv, &count_mutex); printf("watch_count(): thread %ld Condition signal received.\n", my_id); printf("watch_count(): thread %ld count now = %d.\n", my_id, count); } pthread_mutex_unlock(&count_mutex); pthread_exit(NULL); } ////////////////// Main //////////////// int main (int argc, char *argv[]) { int i; long t1=0, t2=1, t3=2, t4=3; pthread_t threads[4]; pthread_attr_t attr; sem_init(&count_sem, 0, 1); /* Initialize mutex and condition variable objects */ pthread_mutex_init(&count_mutex, NULL); pthread_cond_init (&count_threshold_cv, NULL); /* For portability, explicitly create threads in a joinable state */ pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE); pthread_create(&threads[0], &attr, watch_count, (void *)t1); pthread_create(&threads[1], &attr, inc_count, (void *)t2); pthread_create(&threads[2], &attr, inc_count, (void *)t3); pthread_create(&threads[3], &attr, inc_count, (void *)t4); /* Wait for all threads to complete */ for (i=0; i<NUM_THREADS; i++) { pthread_join(threads[i], NULL); } printf ("Main(): Waited on %d threads. Done.\n", NUM_THREADS); /* Clean up and exit */ pthread_attr_destroy(&attr); pthread_mutex_destroy(&count_mutex); pthread_cond_destroy(&count_threshold_cv); pthread_exit(NULL); } I am trying to learn thread scheduling, there is a lot of technical coding that I don't know. I do know in theory how it should work, but having trouble getting started in code... I know, at least I think, this program is not real time and its not meant to be. Some how I need to create a scheduler dispatch to control the threads in the order they should run... RR FCFS SJF ect. Right now I don't have a dispatcher. What I do have is semaphores/ mutex to control the threads. This code does run FCFS... and I have been trying to use semaphores to create a RR.. but having a lot of trouble. I believe it would be easier to create a dispatcher but I dont know how. I need help, I am not looking for answers just direction.. some sample code will help to understand a bit more. Thank you.

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  • replace file with hardlink to another file atomically

    - by Ben Clifford
    I have two directory entries, a and b. Before, a and b point to different inodes. Afterwards, I want b to point to the same inode as a does. I want this to be safe - by which I mean if I fail somewhere, b either points to its original inode or the a inode. most especially I don't want to end up with b disappearing. mv is atomic when overwriting. ln appears to not work when the destination already exists. so it looks like i can say: ln a tmp mv tmp b which in case of failure will leave a 'tmp' file around, which is undesirable but not a disaster. Is there a better way to do this? (what I'm actually trying to do is replace files that have identical content with a single inode containing that content, shared between all directory entries)

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  • getaddrinfo is not statically compiled

    - by bobby
    I have included the header netdb.h, where getaddrinfo is included, but gcc issues this warning: warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking gcc -m32 -static -s -O2 -std=c99 -D_POSIX_C_SOURCE=200112L myprogram.c How can I statically compile whatever file is missing ?

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  • Is O_NONBLOCK being set a property of the file descriptor or underlying file?

    - by Daniel Trebbien
    From what I have been reading on The Open Group website on fcntl, open, read, and write, I get the impression that whether O_NONBLOCK is set on a file descriptor, and hence whether non-blocking I/O is used with the descriptor, should be a property of that file descriptor rather than the underlying file. Being a property of the file descriptor means, for example, that if I duplicate a file descriptor or open another descriptor to the same file, then I can use blocking I/O with one and non-blocking I/O with the other. Experimenting with a FIFO, however, it appears that it is not possible to have a blocking I/O descriptor and non-blocking I/O descriptor to the FIFO simultaneously (so whether O_NONBLOCK is set is a property of the underlying file [the FIFO]): #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> int main(int argc, char **argv) { int fds[2]; if (pipe(fds) == -1) { fprintf(stderr, "`pipe` failed.\n"); return EXIT_FAILURE; } int fd0_dup = dup(fds[0]); if (fd0_dup <= STDERR_FILENO) { fprintf(stderr, "Failed to duplicate the read end\n"); return EXIT_FAILURE; } if (fds[0] == fd0_dup) { fprintf(stderr, "`fds[0]` should not equal `fd0_dup`.\n"); return EXIT_FAILURE; } if ((fcntl(fds[0], F_GETFL) & O_NONBLOCK)) { fprintf(stderr, "`fds[0]` should not have `O_NONBLOCK` set.\n"); return EXIT_FAILURE; } if (fcntl(fd0_dup, F_SETFL, fcntl(fd0_dup, F_GETFL) | O_NONBLOCK) == -1) { fprintf(stderr, "Failed to set `O_NONBLOCK` on `fd0_dup`\n"); return EXIT_FAILURE; } if ((fcntl(fds[0], F_GETFL) & O_NONBLOCK)) { fprintf(stderr, "`fds[0]` should still have `O_NONBLOCK` unset.\n"); return EXIT_FAILURE; // RETURNS HERE } char buf[1]; if (read(fd0_dup, buf, 1) != -1) { fprintf(stderr, "Expected `read` on `fd0_dup` to fail immediately\n"); return EXIT_FAILURE; } else if (errno != EAGAIN) { fprintf(stderr, "Expected `errno` to be `EAGAIN`\n"); return EXIT_FAILURE; } return EXIT_SUCCESS; } This leaves me thinking: is it ever possible to have a non-blocking I/O descriptor and blocking I/O descriptor to the same file and if so, does it depend on the type of file (regular file, FIFO, block special file, character special file, socket, etc.)?

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  • C: lseek() related question.

    - by Andrei Ciobanu
    I want to write some bogus text in a file ("helloworld" text in a file called helloworld), but not starting from the beginning. I was thinking to lseek() function. If I use the following code: #include <unistd.h> #include <fcntl.h> #include <sys/stat.h> #include <sys/types.h> #include <stdlib.h> #include <stdio.h> #define fname "helloworld" #define buf_size 16 int main(){ char buffer[buf_size]; int fildes, nbytes; off_t ret; fildes = open(fname, O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR); if(fildes < 0){ printf("\nCannot create file + trunc file.\n"); } //modify offset if((ret = lseek(fildes, (off_t) 10, SEEK_END)) < (off_t) 0){ fprintf(stdout, "\nCannot modify offset.\n"); } printf("ret = %d\n", (int)ret); if(write(fildes, fname, buf_size) < 0){ fprintf(stdout, "\nWrite failed.\n"); } close(fildes); return (0); } , it compiles well and it runs without any apparent errors. Still if i : cat helloworld The output is not what I expected, but: helloworld Can Where is "Can" comming from, and where are my empty spaces ? Should i expect for "zeros" instead of spaces ? If i try to open helloworld with gedit, an error occurs, complaining that the file character encoding is unknown.

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