01

#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <sys/socket.h>

int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);

如果flag为0相当于accept，flag可以按位或

flag:

SOCK_NONBLOCK:

Set the O_NONBLOCK file status flag on the new open
file description. Using this flag saves extra calls
to fcntl(2) to achieve the same result.

SOCK_CLOEXEC:

Set the close-on-exec (FD_CLOEXEC) flag on the new
file descriptor. See the description of the O_CLOEXEC
flag in open(2) for reasons why this may be useful.

access(2)

#include <unistd.h>

int access(const char *pathname, int mode);

参数：mode

F_OK:文件是否存在可以按位or

R_OK:是否可读

W_OK:可写

X_OK:可执行

返回值：0成功，-1失败errno is set appropriately.

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acct(2) sysctl(8) acct(5)//模糊

功能：acct系统调用可用于启动/禁止进程信息记录功能。

struct acct_v3 {
char ac_flag; /* Flags */
char ac_version; /* Always set to ACCT_VERSION (3) */
u_int16_t ac_tty; /* Controlling terminal */
u_int32_t ac_exitcode; /* Process termination status */
u_int32_t ac_uid; /* Real user ID */
u_int32_t ac_gid; /* Real group ID */
u_int32_t ac_pid; /* Process ID */
u_int32_t ac_ppid; /* Parent process ID */
u_int32_t ac_btime; /* Process creation time */
float ac_etime; /* Elapsed time */
comp_t ac_utime; /* User CPU time */
comp_t ac_stime; /* System time */
comp_t ac_mem; /* Average memory usage (kB) */
comp_t ac_io; /* Characters transferred (unused) */
comp_t ac_rw; /* Blocks read or written
(unused) */
comp_t ac_minflt; /* Minor page faults */
comp_t ac_majflt; /* Major page faults */
comp_t ac_swaps; /* Number of swaps (unused) */
char ac_comm[ACCT_COMM]; /* Command name */
};