用linux命令和程序实际测试一下单进程能打开的最大的句柄数（也可以说是文件数）------并不一定是1024/2048哈

        本文中， 我们继续来做小实验， 看看linux单进程能打开的最大的句柄数（其实也是文件数， 因为linux下一切皆文件嘛）,  命令如下：

xxxxxx:~/network> ulimit -acore file size          (blocks, -c) unlimiteddata seg size           (kbytes, -d) unlimitedscheduling priority             (-e) 0file size               (blocks, -f) unlimitedpending signals                 (-i) 28064max locked memory       (kbytes, -l) 32max memory size         (kbytes, -m) unlimitedopen files                      (-n) 1024pipe size            (512 bytes, -p) 8POSIX message queues     (bytes, -q) 819200real-time priority              (-r) 0stack size              (kbytes, -s) 8192cpu time               (seconds, -t) unlimitedmax user processes              (-u) 28064virtual memory          (kbytes, -v) unlimitedfile locks                      (-x) unlimitedxxxxxx:~/network> xxxxxx:~/network> xxxxxx:~/network> xxxxxx:~/network> ulimit -n1024xxxxxx:~/network> 

       可以看到， 最大文件数是1024.  来写个实际程序测测：

#include <malloc.h>  #include <netinet/in.h>  #include <arpa/inet.h>  #include <sys/ioctl.h>  #include <stdarg.h>  #include <fcntl.h>  #include <fcntl.h>  int main(){int iSock = 0;for(unsigned int i = 0; i < 1050; i++){iSock = socket(AF_INET, SOCK_DGRAM, 0);  // 模拟句柄泄漏printf("iSock is %d\n", iSock);}printf("end\n");return 0;}

      来， 运行看一下：

xxxxxx:~/network> ./a.out iSock is 3iSock is 4iSock is 5iSock is 6iSock is 7iSock is 8iSock is 9iSock is 10iSock is 11iSock is 12iSock is 13iSock is 14iSock is 15iSock is 16iSock is 17iSock is 18iSock is 19iSock is 20iSock is 21iSock is 22iSock is 23iSock is 24iSock is 25iSock is 26iSock is 27iSock is 28iSock is 29iSock is 30iSock is 31iSock is 32iSock is 33iSock is 34iSock is 35iSock is 36iSock is 37iSock is 38iSock is 39iSock is 40iSock is 41iSock is 42iSock is 43iSock is 44iSock is 45iSock is 46iSock is 47iSock is 48iSock is 49iSock is 50iSock is 51iSock is 52iSock is 53iSock is 54iSock is 55iSock is 56iSock is 57iSock is 58iSock is 59iSock is 60iSock is 61iSock is 62iSock is 63iSock is 64iSock is 65iSock is 66iSock is 67iSock is 68iSock is 69iSock is 70iSock is 71iSock is 72iSock is 73iSock is 74iSock is 75iSock is 76iSock is 77iSock is 78iSock is 79iSock is 80iSock is 81iSock is 82iSock is 83iSock is 84iSock is 85iSock is 86iSock is 87iSock is 88iSock is 89iSock is 90iSock is 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922iSock is 923iSock is 924iSock is 925iSock is 926iSock is 927iSock is 928iSock is 929iSock is 930iSock is 931iSock is 932iSock is 933iSock is 934iSock is 935iSock is 936iSock is 937iSock is 938iSock is 939iSock is 940iSock is 941iSock is 942iSock is 943iSock is 944iSock is 945iSock is 946iSock is 947iSock is 948iSock is 949iSock is 950iSock is 951iSock is 952iSock is 953iSock is 954iSock is 955iSock is 956iSock is 957iSock is 958iSock is 959iSock is 960iSock is 961iSock is 962iSock is 963iSock is 964iSock is 965iSock is 966iSock is 967iSock is 968iSock is 969iSock is 970iSock is 971iSock is 972iSock is 973iSock is 974iSock is 975iSock is 976iSock is 977iSock is 978iSock is 979iSock is 980iSock is 981iSock is 982iSock is 983iSock is 984iSock is 985iSock is 986iSock is 987iSock is 988iSock is 989iSock is 990iSock is 991iSock is 992iSock is 993iSock is 994iSock is 995iSock is 996iSock is 997iSock is 998iSock is 999iSock is 1000iSock is 1001iSock is 1002iSock is 1003iSock is 1004iSock is 1005iSock is 1006iSock is 1007iSock is 1008iSock is 1009iSock is 1010iSock is 1011iSock is 1012iSock is 1013iSock is 1014iSock is 1015iSock is 1016iSock is 1017iSock is 1018iSock is 1019iSock is 1020iSock is 1021iSock is 1022iSock is 1023iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1iSock is -1endxxxxxx:~/network> 

       可以看到， 句柄进程号从3-1023， 那 0， 1， 2是什么呢？ 显然是进程的标准输入句柄， 标准输入句柄， 标准错误句柄。 也就是说，  进程打开的句柄是从0, 1, 2, 3, 4, 5, ...一直到1023的， 也就是1024个进程， 和ulimit -n得到的结果完全一致。

       句柄有限， 请你珍惜。

   

       另外要注意的是， 这个1024并不是固定的， 在不同的机器上还不一样， 我另外找了一台机器进行测试， 发现这个值远远大于1024, 如

yyyyyy$ ulimit -n100001

      所以， 这里一定要区分对待。