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Archives for May 2019

“WARNING: Duplicate VG name [vgname]” – error while running LVM commands

by admin

The Problem LVM commands report Duplicate VG names. When vgdisplay is run to check for free space the following message is received: # vgdisplay WARNING: Duplicate VG name testvg2: Existing OEsLyZ-ueap-D66F-6LEB-BKqC-A5B1-exlfZ5 (created here) takes precedence over q7jsuu-f3f8-mVVu-HpMm-FXdK-Xe3Y-d2nVfU The Root Cause Below are a few of the changes which can cause this issue: 1. Some changes […]

Filed Under: CentOS/RHEL 5, CentOS/RHEL 6, CentOS/RHEL 7, Linux

How to Disable Ctrl+c or Ctrl+z Using the “trap” Command in Linux

by admin

The purpose is to disable CTRL+C or CTRL+Z interrupt for the root user or a general user account by the trap command. So basically, when the user tries to interrupt any command or script using CTRL+C or CTRL+Z, he will not be able to do so. The trap command can be used to trap these […]

Filed Under: Linux

How to Disable Daylight Savings Time (DST), and Modify the Timezone on Linux

by admin

Many countries do not follow DST changes, and by default, they are configured so DST time changes alter their system times and even the database times running on them. This post outlines steps to disable DST and modify the timezone on a Linux server. In this example, the time is set as per Brazil country, […]

Filed Under: Linux

How to disable a specific command for a specific user in Linux

by admin

Question: How to prevent a given user from being able to run a specific command. This technique uses a filesystem access control list (ACL) to prevent unwanted access. Caution: The sudo facility is not suitable for this purpose. In particular, “subtracting” an executable from the allowed ALL preset does not work as expected. The example […]

Filed Under: Linux

How To Limit/Restrict FTP Commands On Vsftpd Services (CentOS/RHEL 6,7)

by admin

Learn how to restrict or limit what ftp commands user can run on vsftpd services. For example, how to deny an user to create or remove a directory. 1. The vsftpd services is installed and configured with default options. The creation and elimination of directories is working as expected. # ftp localhost Trying 127.0.0.1… Connected […]

Filed Under: CentOS/RHEL 6, CentOS/RHEL 7, Linux

How To Size UNDO Tablespace For Automatic Undo Management

by admin

Sizing an UNDO tablespace requires three pieces of data. (UR) UNDO_RETENTION in seconds (UPS) Number of undo data blocks generated per second (DBS) Overhead varies based on extent and file size (db_block_size) The undo space needed is calculated as: UndoSpace = UR * (UPS * DBS) Two of the pieces of information can be obtained […]

Filed Under: oracle, Oracle 10g, Oracle 11g

NFSv4 mountpoint shows incorrect ownerships as nobody:nobody in CentOS/RHEL

by admin

The Problem NFSv4 mount incorrectly shows all files with ownership as “nobody:nobody“. From the client server, the mounted NFSv4 share has ownership for all files and directories listed as nobody:nobody instead of the actual user that owns them on the NFSv4 server, or even who created the new file and directory. Also seeing the following […]

Filed Under: CentOS/RHEL 5, CentOS/RHEL 6, Linux

NFSv4 Client Shows “nobody” As Owner And Group For Mount Point (CentOS/RHEL)

by admin

The Problem One or more NFSv4 mount points incorrectly show ownership by “nobody:nobody” instead of the correct ownership. The Solution This is as-designed behavior and not an O/S-related issue. Instead, this is an NFSv3 versus NFSv4 behavioral difference. NFSv3 Behavior In NFSv3, usernames and groupnames are mapped from the UserID (UID) and GroupID (GID) values […]

Filed Under: CentOS/RHEL 5, CentOS/RHEL 6, Linux

ORA-30012 Database Does Not Start With UNDO_MANAGEMENT=AUTO – Oracle Database 11gr2

by admin

The Problem You have set undo_management=AUTO. You have set undo_tablespace = and either this tablespace does not exist or it is not created with ‘undo’ keyword. This may be because you either dropped and did not recreate the undo tablespace or recreated it without specifying ‘undo’ keyword. With this configuration the database will not start […]

Filed Under: oracle, Oracle 11g

How to Create Undo Tablespace for a Newly Added RAC Instance (ORA-30012)

by admin

The Problem A new instance of an existing RAC database was created – not using DBCA. The new database instance will not start. Attempting to start the new instance throws ORA-30012 on startup. ORA-30012: undo tablespace ‘UNDOTBS_02’ does not exist or of wrong type The Solution The new database instance will not start because a […]

Filed Under: oracle

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