20170505

RAID级别

raid0 为带区阵列；
raid1 为镜像阵列
raid0+1 为四块磁盘实现的荣誉磁盘阵列；
raid5 至少三块，容量为（n-1）/n 广泛用于各种服务器：文件，数据库，web，邮件服务器

1.git回退到某个历史版本
1. 使用Git log命令查看所有的历史版本，获取某个历史版本的id，假设查到历史版本的id是139dcfaa558e3276b30b6b2e5cbbb9c00bbdca96。

2. 

[html] view plain copy
git reset --hard 139dcfaa558e3276b30b6b2e5cbbb9c00bbdca96 

3. 把修改推到远程服务器
[javascript] view plain copy
git push -f -u origin maste
因为pythonanywhere上没有 PostgreSQL，所以今天完成的无法在上面实现，但是我上传了，结果报错，所以回退回去了
当然发布更新：
command-line
$ git status
$ git add --all .
$ git status
$ git commit -m "Added views to create/edit blog post inside the site."
$ git push
Then, in a PythonAnywhere Bash console:
command-line
$ cd my-first-blog
$ git pull
[...]
2.Detailed installation guides
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YUM Installation
PostgreSQL can be installed using RPMs (binary) or SRPMs (source) managed by YUM. This is available for the following Linux distributions (both 32- and 64-bit platforms; for the current release and prior release or two):
Fedora
Red Hat Enterprise Linux
CentOS
Scientific Linux
Oracle Enterprise Linux
See links from the main repository, http://yum.postgresql.org:
A list of available packages
Repository packages for different version combinations
Status of RPM builds
Contents [hide] 
1 Instructions
1.1 Configure your YUM repository
1.2 Install PGDG RPM file
1.3 Install PostgreSQL
1.4 Post-installation commands
1.4.1 Data Directory
1.4.2 Initialize
1.4.3 Startup
1.5 Control service
2 Removing
3 Support
4 After installation
Instructions

Configure your YUM repository
Locate and edit your distributions .repo file, located:
On Fedora: /etc/yum.repos.d/fedora.repo and /etc/yum.repos.d/fedora-updates.repo, [fedora] sections
On CentOS: /etc/yum.repos.d/CentOS-Base.repo, [base] and [updates] sections
On Red Hat: /etc/yum/pluginconf.d/rhnplugin.conf [main] section
To the section(s) identified above, you need to append a line (otherwise dependencies might resolve to the postgresql supplied by the base repository):
exclude=postgresql*
Install PGDG RPM file
A PGDG file is available for each distribution/architecture/database version combination. Browse https://yum.postgresql.org/repopackages.php and find your correct RPM. For example, to install PostgreSQL 9.6 on CentOS 7 64-bit: yum install https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/pgdg-redhat96-9.6-3.noarch.rpm
Install PostgreSQL
To list available packages:
yum list postgresql*
For example, to install a basic PostgreSQL 9.6 server:
yum install postgresql96-server
Other packages can be installed according to your needs.
Post-installation commands
After installing the packages, a database needs to be initialized and configured.
In the commands below, the value of <name> will vary depending on the version of PostgreSQL used.
For PostgreSQL version 9.0 and above, the <name> includes the major.minor version of PostgreSQL, e.g., postgresql-9.4

Data Directory
The PostgreSQL data directory contains all of the data files for the database. The variable PGDATA is used to reference this directory.
The default data directory is:
/var/lib/pgsql/<name>/data
For example:
/var/lib/pgsql/9.6/data
Initialize
The first command (only needed once) is to initialize the database in PGDATA.
For Red Hat 6:
service <name> initdb
E.g. for version 9.6:
service postgresql-9.6 initdb
For Red Hat 7, and Fedora 23 and above:
If the previous command did not work, try directly calling the setup binary, located in a similar naming scheme:
/usr/pgsql-y.x/bin/postgresqlyx-setup initdb
E.g. for version 9.6:
/usr/pgsql-9.6/bin/postgresql96-setup initdb

Startup
If you want PostgreSQL to start automatically when the OS starts, do the following:
In RHEL 6 and PostgreSQL 9.6:
chkconfig postgresql-9.6 on
In RHEL 7+, and Fedora 23+ try:
systemctl enable postgresql-9.6.service
Control service
To control the database service, use:
for RHEL 5 and 6:
service <name> <command>
where <command> can be:
start : start the database
stop : stop the database
restart : stop/start the database; used to read changes to core configuration files
reload : reload pg_hba.conf file while keeping database running
E.g. to start version 9.6:
service postgresql-9.6 start

With RHEL 7.1+ and CentOS 7.1+, and Fedora 23+, systemd is introduced. Use this instead:
systemctl enable postgresql-9.6.service
systemctl start postgresql-9.6.service
Removing

To remove everything:
yum erase postgresql96*
or 
dnf remove postgresql96* for Fedora 23+.
Or remove individual packages as desired.
Support

Email: pgsql-pkg-yum@postgresql.org (requires subscription)
After installation
sudo su - postgres
Or the more modern form:

sudo -u postgres -i
Out of all the answers above nothing worked for me. I had to manually change the users password in the database and it suddenly worked.

psql -U postgres -d postgres -c "alter user produser with password 'produser';"
I used the following settings:

pg_hba.conf

local all all peer
# IPv4 local connections:
host all all 127.0.0.1/32 password 
# IPv6 local connections:
host all all ::1/128 password
Connection is successful finally for the following command:

psql -U produser -d dbname -h localhost -W 

这其中会出现用户找不到的问题，所以下面是解决方法
3.今天实现评论的功能，但是在本地！！！！