linux thread how to know the memory usage

PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
13153 webmaster 15 0 57348 55M 4164 S 0.0 3.7 0:31 0 httpd
15534 webmaster 21 0 49612 48M 5028 S 0.1 3.2 0:32 0 httpd
27383 mysql 15 0 66800 45M 1724 S 1.9 3.0 368:01 0 mysqld
19931 webmaster 21 0 41928 40M 5020 S 0.3 2.7 0:16 0 httpd
18903 webmaster 15 0 39348 38M 5016 S 0.3 2.5 0:22 0 httpd
8932 root 15 0 23036 22M 2960 S 0.0 1.4 0:20 0 httpd
26942 webmaster 24 0 13672 13M 2168 R 8.9 0.8 0:00 0 web.cgi

From the >top on linux OS, how to calculate the memory usage,
what the SIZE,RSS,SHARE

 

 

 

 

Top