Happy Mom and Dad’s Day – The Living Years
Long time no listen. Finally found out. Happy Mom and Dad’s Day.
YouTube – Mike & The Mechanics – The Living Years
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FTP Active Mode vs. Passive Mode
Since we need to deal with firewall between FTP clients and server, the following diagram shows that two modes of FTP. So, we can design more accuracy firewall policy by applying different modes.
The following is quoted the pros and cons:
Active FTP is beneficial to the FTP server admin, but detrimental to the client side admin. The FTP server attempts to make connections to random high ports on the client, which would almost certainly be blocked by a firewall on the client side. Passive FTP is beneficial to the client, but detrimental to the FTP server admin. The client will make both connections to the server, but one of them will be to a random high port, which would almost certainly be blocked by a firewall on the server side.
vsftpd put “553 Could not create file” solution
I set up a new FTP server by using vsftpd. I observed that I could get file but failed to upload file. After investigation, I found out there are three points I should concern about.
First, write_enable=YES in /etc/vsftpd/vsftpd.conf
Second, system-config-firewall to enable command port 21 and data port 20.
Last, system-config-selinux to set Boolean ftp_home_dir to 1
After service vsftpd restart, I can get and put file in my home directory.
tftpboot directory changed in FC9
One change in FC9 is tftpboot directory. In the previous release, after installed tftp-server, it created /tftpboot directory. In FC9, the directory change to /var/lib/tftpboot/. The reason I guess is to keep root directory more clear.
UTF-8 to UTF-16 Mapping
UTF-8 to UTF-16
| UTF-8 Pattern | UTF-16 High Byte | UTF-16 Low Byte |
|---|---|---|
| 0tuvwxyz | 00000000 | 0tuvwxyz |
| 110pqrst 10uvwxyz |
- 00000pqr |
- stuvwxyz |
| 1110jklm 10npqrst 10uvwxyz |
- - jklmnpqr |
- - stuvwxyz |
| 11110efg 10hijklm 10npqrst 10uvwxyz |
- 110110ab - 110111qr |
- cdjklmnp - stuvwxyz |
Reference: Cameron, R. “A Case Study in SIMD Text Processing with Parallel Bit Streams”, School of Computing Science, SFU, 2008
Unicode Range to UTF-16 Pattern
Using one table to express RFC 2781
Unicode to UTF-16
| Unicode Range | Code Point Pattern | UTF-16 Pattern |
|---|---|---|
| 0000-007F | 00000 00000000 0tuyvwxyz | 00000000 0tuvwxyz |
| 0800-FFFF | 00000 00000pqr stuvwxyz | 00000pqr stuvwxyz |
| 0800-FFFF | 00000 jklmnpqr stuvwxyz | jklmnpqr stuvwxyz |
| 10000-10FFFF | efghi jklmnpqr stuvwxyz | 110110ab cdjklmnp 110111qr stuvwxyz |
C/C++: srand() and rand() to get random numbers
We can simply design a 6/49 lottery selector by randomly get numbers from 1 to 49. We will use srand() and rand().
srand() initializes random generator by argument seed. Normally, we use time() as seed.
srand( (unsigned int) time( (time_t *) NULL) );
rand() is function call to generate numbers which initialized some distinctive value using srand(). We can get number from 1 to 49 by mod 49 and plus 1.
(rand() % 49) + 1;
C/C++: Swap Two Value by XOR
#include<stdio.h>
int
main()
{
int one=20;
int two=21;
one ^= two;
two ^= one;
one ^= two;
printf(“new one is:%d, new two is:%d\n”, one, two);
return 0;
}
C/C++: #define
#define is precompile directive for compiler. Basically, #define has three functionalities, text substitutions, macro and conditional compiler directives.
1. Define Text Substitutions
#define MAXNUMBER 1024
#define BUFFER 2048
#define TRUE 1
#define FALSE 0
2. Define Macro
#define mem_clear(name) memset( name, ‘ ‘, sizeof(name))
#define max(a, b) ( (a) > (b) ? (a) : (b) )
However, sometimes, define macro do have some drawbacks. If “a” is “++i” in above definition, the “i” will be increment two times. Macro doesn’t have memory address. Macro doesn’t have recursive algorithm. Thus, Macro is hard to debug.
3. Conditional Precompile Directive
This feature has more advantage. we can put #ifdef, #ifndef and #endif in anywhere in the body of program. It will cooperate with configuration file to realize the certain functions.
#ifdef FAST_FUNC
#ifndef BUFFERED_FUNC
rslt = func((char **) &srcbuf_ptr,
&inbytes_left,
(char **) &trgtbuf_ptr,
&outbytes_left);
#endif
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