#include <stdio.h>

#include <unistd.h>

int main () {

  int real = getuid();

  int euid = geteuid();

  printf("The REAL UID =: %d\n", real);

  printf("The EFFECTIVE UID =: %d\n", euid);

  sleep(100);

}

$ cc test.c

$ ./a.out

The REAL UID =: 1000

The EFFECTIVE UID =: 1000

$ sudo chown root a.out

$ sudo chmod 4755 a.out

$ ./a.out

The REAL UID =: 1000

The EFFECTIVE UID =: 0

(대기)

$ ps -eo pid,euser,ruser,comm | grep a.out
PID EUSER    RUSER    COMMAND

 4481 root     deploy   a.out

Set<String> s1 = Sets.newHashSet("1", "2", "3");

Set<String> s2 = Sets.newHashSet("3", "4");

System.out.println(Sets.difference(s1, s2)); // 1,2

Set<String> set1 = ((Set<String>) ((HashSet<String>) s1).clone());

set1.removeAll(s2);

System.out.println(set1); // 1, 2

System.out.println(com.google.common.collect.Sets.difference(s1, s2)); // 1,2

System.out.println(Sets.symmetricDifference(s1, s2)); // 1, 2, 4

ESTABLISHED off (0.00/0/0)

ESTABLISHED keepalive (239.12/0/0)

getmerge

Usage: hadoop fs -getmerge [-nl] <src> <localdst>

Takes a source directory and a destination file as input and concatenates files in src into the destination local file. Optionally -nl can be set to enable adding a newline character (LF) at the end of each file.

Examples:

• hadoop fs -getmerge -nl /src /opt/output.txt
• hadoop fs -getmerge -nl /src/file1.txt /src/file2.txt /output.txt

Exit Code:

Returns 0 on success and non-zero on error.

$ hdfs dfs -ls /tmp/test/20160418

Found 6 items

/tmp/test/_SUCCESS

/tmp/test/done

/tmp/test/part-m-00000

/tmp/test/part-m-00001

/tmp/test/part-m-00002

/tmp/test/part-m-00003

$ hdfs dfs -getmerge hdfs://google-hadoop장비이름/tmp/test/20160418  /tmp/1

$ ls  /tmp/1

/tmp/1

select timezone, count(*) as count from request where date=20160401

 group by timezone order by count desc limit 30

hive> CREATE TABLE users (`id` int, `location` string);

OK

hive> desc users;

OK

col_name data_type comment

id                   int

location             string

hive> ALTER TABLE users RENAME TO new_users;

OK

hive> desc new_users;

OK

col_name data_type comment

id                   int

location             string

Time taken: 0.036 seconds, Fetched: 2 row(s)

hive> ALTER TABLE users SET TBLPROPERTIES ('comment' = 'new user heros');

OK

hive> ALTER TABLE  users ADD COLUMNS (`work` string COMMENT 'comment');

OK

Time taken: 0.108 seconds

hive> desc users;

OK

col_name data_type comment

id                   int

location             string

work                 string               comment

Time taken: 0.104 seconds, Fetched: 3 row(s)

hive> ALTER TABLE  users ADD COLUMNS (`has_talk` string COMMENT 'checking whether user has talk', `json` string);

OK

Time taken: 0.041 seconds

hive> desc users;

OK

col_name data_type comment

id                   int

location             string

work                 string               comment

has_talk             string               checking whether user has talk

json                 string

Time taken: 0.036 seconds, Fetched: 5 row(s)

hive> ALTER TABLE users CHANGE work work_name string AFTER json;

OK

Time taken: 0.047 seconds

hive> desc users;

OK

col_name data_type comment

id                   int

location             string

has_talk             string               checking whether user has talk

json                 string

work_name           string               comment

Time taken: 0.039 seconds, Fetched: 5 row(s)

hive> ALTER TABLE users REPLACE COLUMNS (`id` int, `location` string);

OK

Time taken: 0.071 seconds

hive> desc users;

OK

col_name data_type comment

id                   int

location             string

Time taken: 0.05 seconds, Fetched: 2 row(s)

필드명은 `로 사용하고, 주석은 '로 사용한다.