System auditing with auditd System auditing is a very important task that should be a part of every server. It allows us to audit minute details related to what exactly is happening within the system. auditd is a userspace component to the Linux auditing system. This means that system users will be able to run auditd to configure rules and alerts for auditing functionality with the Linux system. One of the best things about auditd is that it is tightly integrated with the kernel, so it gives … [Read more...] about Audit rules for monitoring Copy, move, delete and kill Commands In Linux
Archives for October 2018
How to Verify if ALUA Mode is Enabled on a LUN in CentOS/RHEL
What is ALUA? ALUA stands for Asymmetrical Logical Unit Access. Midrange arrays usually have an internal interconnect between the two storage processors used for write cache mirroring and other management purposes. ALUA was an addition to the SCSI standard that enables a LUN to be presented via its primary path and via an asymmetrical (significantly slower) path via the secondary storage processor, transferring the data over the internal interconnect. In simpler terms, ALUA specifies a type … [Read more...] about How to Verify if ALUA Mode is Enabled on a LUN in CentOS/RHEL
“mlock failed: Cannot allocate memory” lvcreate command error in CentOS/RHEL 7
The Problem When attempting to create an LV the following error occurs. # lvcreate -L 5G -n apps vgOS 7fa0c6cd2000-7fa0c6cd3000 r-xp 00216000 fd:00 8388746 /usr/lib64/libgcc_s-4 .8.5-20150702.so.1: mlock failed: Cannot allocate memory 7fa0c75ce000-7fa0c75cf000 r-xp 00265000 fd:00 8895769 /usr/lib64/libdevmapp er.so.1.02: mlock failed: Cannot allocate memory 7fa0c77d6000-7fa0c77d7000 r-xp 00207000 fd:00 9313347 /usr/lib64/libdevmapp er-event.so.1.02: mlock failed: Cannot allocate … [Read more...] about “mlock failed: Cannot allocate memory” lvcreate command error in CentOS/RHEL 7
How to avoid the “promiscuous mode” messages being logged repeatedly in /var/log/messages
The ask How to suppress messages like "... entered promiscuous mode" or "... left promiscuous mode" ? For example: device eth3 entered/left promiscuous mode repeatedly in syslog - /var/log/messages: Aug 14 12:01:29 ol6-server kernel: [56113.819404] device eth3 entered promiscuous mode Aug 14 12:53:01 ol6-server kernel: [59198.608207] device eth3 left promiscuous mode Aug 14 12:53:03 ol6-server kernel: [59200.722148] device eth3 entered promiscuous mode Aug 14 16:01:51 ol6-server kernel: … [Read more...] about How to avoid the “promiscuous mode” messages being logged repeatedly in /var/log/messages
How to Configure Interface(s) in promiscuous mode on CentOS/RHEL 7 (persistently)
What is Promiscuous mode Promiscuous mode or promisc mode is a feature that makes the ethernet card pass all traffic it received to the kernel. It is usually used by a packet sniffing program like Wireshark, and tcpdump. If there was such program intentionally running or bridged networking for hardware virtualization, the "promiscuous mode" message might be simply ignored. Otherwise, deep investigation on that system will be required due to a security issue. When there is no audit daemon … [Read more...] about How to Configure Interface(s) in promiscuous mode on CentOS/RHEL 7 (persistently)
“Abort command issued nexus” error messages in /var/log/messages file
The Problem What do the "Abort command issued nexus" error messages in /var/log/messages file mean? Nov 21 07:08:58 kernel: qla2xxx [0000:49:00.0]-801c:4: Abort command issued nexus=4:3:33 -- 1 2002. Nov 21 07:08:58 kernel: qla2xxx [0000:49:00.0]-801c:4: Abort command issued nexus=4:1:33 -- 1 2002. Nov 21 07:08:59 kernel: qla2xxx [0000:49:00.0]-801c:4: Abort command issued nexus=4:1:68 -- 1 2002. Nov 21 07:08:59 kernel: qla2xxx [0000:49:00.0]-801c:4: Abort command issued nexus=4:2:16 -- … [Read more...] about “Abort command issued nexus” error messages in /var/log/messages file
Oracle ASM 12c – New Features with examples
This post discusses a few 12C ASM new features with examples: Failgroup_repair_time Online disk replace Estimate Work V$ASM_OPERATION view 1. FAILGROUP_REPAIR_TIME For earlier ASM versions, we had disk_repair_time, from 12C onwards we have failgroup_repair_time at the ASM level. Because failure group outages are more likely to be transient in nature and because replacing all the disks in a failure group is a much more expensive operation than replacing a single disk, it would … [Read more...] about Oracle ASM 12c – New Features with examples
Oracle Database 12c New Feature – RMAN “RECOVER TABLE”
Table recovery Table recovery was possible in earlier releases as well. Until previous releases, if we wanted to recover a table, we had the following options: Database point in time recovery (DBPITR) Tablespace point in time recovery (TSPITR) Flashback technology The RECOVER TABLE command is a new feature in 12C that allows a point in time recovery of a table or a table partition. The table is recovered into an auxiliary instance and there is the option to: import the recovered … [Read more...] about Oracle Database 12c New Feature – RMAN “RECOVER TABLE”
Interview Questions : Oracle Flex ASM 12c
What is Oracle Flex ASM? Oracle Flex ASM is an ASM instance which will be running in the cluster based on cardinality defined. The default cardinality is three, but you can change it using srvctl modify asm command. It means that ASM is not required to run on each node in the cluster. In the previous release, ASM will be running on each node in the cluster and ASM clients (Database, ACFS, ADVM) can only access ASM by using an ASM on the same host. With Oracle Flex ASM, the clients can … [Read more...] about Interview Questions : Oracle Flex ASM 12c
Oracle sql script to report the list of files stored in ASM and CURRENTLY NOT OPENED
Purpose One of the features of ASM is databases consolidation. A single diskgroup will be the repository for multiple databases. The result, having a large number of datafiles. If the files were created using OMF (Oracle Managed Files) format, when the datafile is deleted on the database side, it is also deleted on the ASM side. There may be situations when the datafiles are not deleted on the ASM side, particularly when not using OMF format. With large diskgroups holding large number of … [Read more...] about Oracle sql script to report the list of files stored in ASM and CURRENTLY NOT OPENED