list all running services
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service --status-all |
Check Running Services on CentOS
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Drop Cache in Linux
Since kernel 2.6.16, a utility has been provided to allow the system to drop the page cache and/or inode and dentry caches on command, which can help free up a lot of memory.
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Java HTTP client crashes on HTTPS connections
OS: CentOS 6.5
JAVA: 1.7.0_91
One use case in the project: due to the remote client server system upgrade, HTTPClient runs into such exception like javax.net.ssl.SSLException: java.security.ProviderException: java.security.KeyException:
Install Java 8 (JDK 8u66) on CentOS
Download latest 64 bit Java SE Development Kit 8 release
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# mkdir /opt/shared # cd /opt/shared # wget --no-cookies --no-check-certificate --header "Cookie: gpw_e24=http%3A%2F%2Fwww.oracle.com%2F; oraclelicense=accept-securebackup-cookie" "http://download.oracle.com/otn-pub/java/jdk/8u66-b17/jdk-8u66-linux-x64.tar.gz" # tar xzf jdk-8u66-linux-x64.tar.gz |
Application Transport Security in iOS programming
App Transport Security (ATS) lets an app add a declaration to its Info.plist file that specifies the domains with which it needs secure communication. ATS prevents accidental disclosure, provides secure default behavior, and is easy to adopt. You should adopt ATS as soon as possible, regardless of whether you’re creating a new app or updating an existing one.
If you’re developing a new app, you should use HTTPS exclusively. If you have an existing app, you should use HTTPS as much as you can right now, and create a plan for migrating the rest of your app as soon as possible.
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Problem: unable to execute /bin/rm: Success
In Linux environment, when you want to delete the files under one directory, you might see:
“sudo: unable to execute /bin/rm: Success”
Reason: too many files under the directory
Solution:
sudo find . -name ‘*’ -exec rm {} \;
Which way she is spinning? left brain or right brain?
Which way she is spinning?
If you are seeing her turning counter-clockwise, you are probably are more left brain thinker. Otherwise, you are mostly more right brained.
How HashSet implemented in Java
In Java, HashSet uses HashMap to finish: add, get, iterator etc. The HashMap also can help an element inside HashSet is unique.
How HashMap works in Java
HashMap works on the principle of Hashing. There are several terms: key, hash code, hash function, bucket, entry in HashMap
Forward Proxy vs Reverse Proxy
A forward proxy provides proxy services to a client or a group of clients while a reverse proxy proxies in behalf of servers.
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