In snmpd.c there is the following, rather odd piece of code:
if (pid_file != NULL) {
/*
* unlink the pid_file, if it exists, prior to open. Without
* doing this the open will fail if the user specified pid_file
* already exists.
*/
unlink(pid_file);
fd = open(pid_file, O_CREAT | O_EXCL | O_WRONLY, 0600);
if (fd == -1) {
snmp_log_perror(pid_file);
if (!netsnmp_ds_get_boolean(NETSNMP_DS_APPLICATION_ID,
NETSNMP_DS_AGENT_NO_ROOT_ACCESS)) {
exit(1);
}
} else {
if ((PID = fdopen(fd, "w")) == NULL) {
snmp_log_perror(pid_file);
exit(1);
} else {
fprintf(PID, "%d\n", (int) getpid());
fclose(PID);
}
close(fd);
}
}
What is the purpose of unlink followed by open(,O_CREAT|O_EXCL,)?
Why not use just open(,O_CREAT|O_TRUNC,)?
Why is it not an error to fail to open the pid file if the agent runs
without root access?
I posit that this code is equivalent to the one above (sans a small race
window and the removal of the non-root pid file special handling)
if ((PID=fopen(pid_file, "w")) == NULL) {
snmp_log_perror(pid_file);
exit(1);
} else {
fprintf(PID, "%d\n", (int) getpid());
fclose(PID);
}
/MF
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