Change default password for Oracle 11g Database

oracle11g
To change the default password for SYS and SYSTEM users use the trick.

1. Run in shell:

sqlplus  / as sysdba

2. Change password for SYS:

SQL> alter user SYS identified by "your-super-password";

3. Change password for SYSTEM:

SQL> alter user SYSTEM identified by "your-super-password";

Thanx to http://stackoverflow.com/a/740884

Using RSYNC to backup (synchronize) folders

rsync
If you want to synchronize two folders use next snippets.

1. Sync folder “source” content to “target” folder:

rsync -arpv --delete /mnt/source/ /mnt/target

Notice trailing slash for “source” folder!

2. Sync whole folder “source” to “parent” folder:

rsync -arpv --delete /mnt/source /mnt/parent

More info https://linux.die.net/man/1/rsync

Generate SSH key (identity)

ssh
To generate SSH key you have to do following:

1. Install any SSH client (if absent).

2. Show existing keys:

ls -la ~/.ssh

It can be empty.

3. Generate key itself:

ssh-keygen -t rsa -b 4096 -C "your@email.com"

You’ll be prompted to enter the path to store the key. Also, you can enter a passphrase. But it can be empty in some cases.

4. Check for new key:

ls -la ~/.ssh

You’ll see something like:

-rw-r–r– 1 dtv 197121 1679 jun 11 2016 id_rsa
-rw-r–r– 1 dtv 197121 400 jun 11 2016 id_rsa.pub

5. Run SSH agent to add new key:

eval "$(ssh-agent -s)"

6. Add SSH key:

ssh-add ~/.ssh/id_rsa

Thanx to https://help.github.com/articles/generating-an-ssh-key/

Multiple SSH keys configuration

ssh-keys
If you are using, for example GIT, it may be needed to use different ssh keys for different servers. By default git client uses “~/.ssh/id_rsa” private key.
And you’ll get the error like:

Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.

If you want to use another ssh key, you should load it before with ssh-add command each time.

To avoid the issue you can specify the ssh key for certain server.
Just create (or update) file “~/.ssh/config” with content:

Host  someserver.com
  HostName                  someserver.com
  Port                      22
  PreferredAuthentications  publickey
  IdentityFile              "C:\Users\user42\.ssh\private-ssh-key-file"

Thanx to
https://confluence.atlassian.com/bitbucket/configure-multiple-ssh-identities-for-gitbash-mac-osx-linux-271943168.html
and https://gist.github.com/jexchan/2351996

Apache and SVN configuration with user permissions

apache-svn
This tutorial shows how to configure Apache+SVN couple.

1. First of all you should install Apache Httpd server (version 2.4 in this case) with DAV_SVN module and subversion client:

yum -y install httpd mod_dav_svn subversion

2. Check installed modules are turned on:

LoadModule auth_basic_module modules/mod_auth_basic.so
LoadModule authn_core_module modules/mod_authn_core.so
LoadModule authz_user_module modules/mod_authz_user.so

LoadModule dav_module modules/mod_dav.so
LoadModule dav_fs_module modules/mod_dav_fs.so
LoadModule dav_lock_module modules/mod_dav_lock.so

LoadModule dav_svn_module     modules/mod_dav_svn.so
LoadModule authz_svn_module   modules/mod_authz_svn.so
LoadModule dontdothat_module  modules/mod_dontdothat.so

3. Configure repository folder in http.conf:

<Directory "/srv/svn/repos">
    Options None
    AllowOverride None
    Require all granted
</Directory>

4. Add virtual host:

<VirtualHost *:80>
    ServerName svn.domain.com
    DocumentRoot "/srv/svn"
    ErrorLog "/srv/svn/log/svn.domain.com_error_log"
    CustomLog "/srv/svn/log/svn.domain.com_access_log" common
    TransferLog "/srv/svn/log/svn.domain.com_transfer_log"

    LimitXMLRequestBody 0
    LimitRequestBody 0

    <Location />
        DAV svn
        SVNParentPath "/srv/svn/repos"
        SVNListParentPath on
        AuthType Basic
        AuthName "Subversion repository"
        AuthUserFile "/srv/svn/svn.passwd"
        AuthzSVNAccessFile "/srv/svn/svn.access"
        Require valid-user
    </Location>
</VirtualHost>

5. Create passwd file “/srv/svn/svn.passwd”:

htpasswd -c -b /srv/svn/svn.passwd tom tomPasswordHere
htpasswd -b /srv/svn/svn.passwd jerry jerryPasswordHere
htpasswd -b /srv/svn/svn.passwd spike spikePasswordHere

6. Create access file “/srv/svn/svn.access”:

[groups]
adminGroup = tom
otherGroup = jerry,spike

[/]
* =
@adminGroup = rw

[php:/project42]
@otherGroup = rw

[php:/projectGood]
@otherGroup = r

So, as you see adminGroup has full access to php repository.
But otherGroup has write access to project42 and only read permissions on projectGood.

Also see http://stackoverflow.com/questions/81361/how-to-setup-access-control-in-svn

Subversion (SVN) tricks

subversion_logo-384x332
When you use Subversion as a source control management system it is useful to know some magic commands.

The next command cleans, updates, adds and shows status of local repository:

  svn cleanup \
    && echo "-UPDATE-" && svn up \
    && echo "-ADD-" && svn add * --force \
    && echo "-STATUS-" && svn st

After you can commit changes with:

  svn ci -m "your comment..."

More info on https://subversion.apache.org/ and http://svnbook.red-bean.com/

Remove kernel in CentOS

kernel
After unsuccessful upgrade of kernel you have to fix linux OS.
To delete invalid kernel in case of CentOS do next steps.

1. Show kernel list:

  rpm -q kernel

And you’ll see output:

  kernel-3.10.0-229.14.1.el7.x86_64
  kernel-3.10.0-229.20.1.el7.x86_64
  kernel-3.10.0-327.3.1.el7.x86_64
  kernel-3.10.0-327.4.4.el7.x86_64
  kernel-3.10.0-327.22.2.el7.x86_64

2. Delete corrupted kernel:

  rpm -e kernel-3.10.0-327.22.2.el7.x86_64

3. Reboot.
So, you system downgraded!

Thanx to http://blog.zwiegnet.com/linux-server/delete-oldcorrupt-linux-kernel-centos/