Question

My program has a loop that runs initUSB() and then runs writeEssentials() multiple times.
initUSB() is a function that mounts the USB to a directory.
writeEssentials() is a function that opens a file, and appends it with data, and then closes the file.

After a minute or so after the initial run of the program, the program will report that the file system is “read only”, and will refuse to write anymore data, until initUSB() is run again. This happens weather or not I fprintf() into the file pointer. As a temporary solution, I made writeEssentials() remount the drive if it becomes read-only. This works, but I would rather not remount the drive every minute.

Why does this happen, and how can I fix this error?

The program is running on an Debian embedded Linux system, on a TS-7800.

InitUSB:

int initUSB(){
int i;
FILE * filecheck = fopen(HMITelemCheckFile, "r");
for(i = 0; i < 26; i++) {
    char usbMountFromPathTry[256];
    char sdanum[5];
    strcpy(usbMountFromPathTry, usbMountFromPath);
    sprintf(sdanum, "%c1", i+'a');
    strcat(usbMountFromPathTry, sdanum);
    if(!mount(usbMountFromPathTry, usbMountToPath, "vfat", (long)NULL, NULL)){
        printf("Mount successful\n");
        return 1;
    } else if(!mount(usbMountFromPathTry, usbMountToPath, "vfat", MS_REMOUNT, NULL)){
        printf("Mount successful\n");
        return 1;
    }
    printf("Mount error: ");
    printf("%s\n", usbMountFromPathTry);
}
printf("Mount ERROR\n");
return 0;
}

writeEssentials():

void writeEssentials(){
FILE * file = fopen(usbMountEssentials, "a+");
fflush(file);
perror("file");
if(file == NULL){
    initUSB();
    printf("null file\n");
    return;
}
fprintf(file, "\n%s, ", getDate());
fprintf(file, "%s, ", getTime());
fprintf(file, "%1.2f, ", getSpeed());
fprintf(file, "%d, ", getRPM());
fprintf(file, "%d, ", getRegen());
fprintf(file, "%d, ", getAirgap());
fprintf(file, "%d, ", getBattery());
fprintf(file, "%.2f, ", *(getADCTemps()+COMPUTER_BOX_TEMP_INDEX));
fprintf(file, "%.2f, ", *(getBMS()+BMS_TEMP_INDEX+(BMS_NUM_VAR*0)));
fprintf(file, "%.2f, ", *(getBMS()+BMS_TEMP_INDEX+(BMS_NUM_VAR*1)));
fprintf(file, "%.2f, ", *(getBMS()+BMS_TEMP_INDEX+(BMS_NUM_VAR*2)));
fprintf(file, "%.2f, ", *(getMPPT()+MPPT_TEMP_INDEX+(MPPT_NUM_VAR*0)));
fprintf(file, "%.2f, ", *(getMPPT()+MPPT_TEMP_INDEX+(MPPT_NUM_VAR*1)));
fprintf(file, "%.2f, ", *(getMPPT()+MPPT_TEMP_INDEX+(MPPT_NUM_VAR*2)));
fprintf(file, "%.2f, ", *(getMPPT()+MPPT_TEMP_INDEX+(MPPT_NUM_VAR*3)));
fprintf(file, "%s, ", getLat());
fprintf(file, "%s, ", getLong());
int i;
for(i = 0; i < getNumErrors(); i++){
    //fprintf(file, "%s, ", getErrorText(*(getErrors()+i)));
}
fclose(file);
perror("close file error");
}

Answer 1

Check dmesg. Filesystems spontaneously going read-only is usually an indication that there’s some corruption that’s being detected, so the kernel is setting the FS as read-only to protect it from further damage.