Plain vanilla is an adjective describing the simplest version of something, without any optional extras, by analogy with vanillaice cream, the default flavour.
- Name servers host a domain’s DNS information in a text file called the zone file. They’re are also known as Servers of
- On Linux (and probably most Unix), there is no OS-level DNS caching unless nscd is installed and running. Even then, the DNS caching feature of nscd is disabled by default at least in Debian because it's broken. The practical upshot is that your linux system very very probably does not do any OS-level DNS caching.
- An AAAA record is just like an A record, but for IPv6 IP addresses. A typical AAAA record looks like the following:
Memory Analyzer can currently work with three dump types:
- IBM Portable Heap Dump (PHD): This proprietary IBM format contains
only the type and size of each Java object in the process, and the
relationships among the objects. This dump-file format is
significantly smaller than the other formats and contains the least
information. The data is usually sufficient, though, for diagnosing
memory leaks and getting a basic understanding of the application's
architecture and footprint.
- HPROF binary dump: The HPROF binary format contains all the data
present in the IBM PHD format as well as the primitive data held
inside the Java objects, and the thread details. You can look at the
values held in fields inside the objects and see which methods were
being executed at the time the dump was taken. The additional
primitive data makes HPROF dumps significantly larger than
PHD-format dumps; they are approximately the same size as the used
- IBM system dumps: When the IBM Java runtime is being used, the
native operating-system dump file — a core file on AIX® or Linux, a
minidump on Windows®, or a SVC dump on z/OS®— can be loaded into
Memory Analyzer. These dumps contain the entire memory image of the
running application — all the information and data in the HPROF
format, as well as all of the native-memory and thread information.
This is the largest and most comprehensive dump-file format.
Both IBM dump types are available only with the Diagnostic Tool Framework for Java (DTFJ) plug-in installed
nc (netcat) - arbitrary TCP and UDP connections and listens
-words [-46DdhklnrStUuvz] [-i interval] [-p source_port] [-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_protocol] [Xo -x proxy_address[: port]] [hostname] [port[s]]
nc -wz baidu.com
mtr - a network diagnostic tool
mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
mtr -rw example.com
iostat reports CPU, disk I/O, and NFS statistics.
vmstat reports virtual memory statistics.
mpstat reports processors statictics.
vmstat: Virtual Memory statistic. 实时收集并报告主内存,交换分区(SWAP)以及 CPU 的使用情况. 用来查找和定位内存的性能问题.
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 1 0 0 90175 239 1434 0 0 0 1 3 2 0 0 100 0 0 0 0 0 90175 239 1434 0 0 0 0 153 176 0 0 100 0 0 1 0 0 90151 239 1434 0 0 0 4 3068 1961 1 2 97 0 0
r: process running
b: process blocked
swpd: swapped to swap
free: memory free
buff: memory committed
cache: declared or can be swapped to swap
si: swap in
so: swap out
bi: block in (read disk unit is block, memory unit is page)
bo: block out
cs: context switch
us: user, sd: system/kernel, id: idle, ws: waste