Question: How to send emails to external users with mailx running on CentOS/RHEL system? The following command shows how to send a mail to an external user using mailx: # echo "this is the body of the email" | mailx -vvv -s "test mail" -r "From" -S smtp="your-smtp" someone@address Here, -vvv = Verbosity. -s = Specifies the subject. -r = Email sent from. -S = Specifies the smtp server. To be able to send mails out of the internal network using … [Read more...] about How To Send Mails To an External User With Mailx on Linux
How to Replace a Failed Btrfs Device
The Problem Originally the btrfs file system is build on multiple disks. # btrfs filesystem show Label: 'MYBTRFS' uuid: 09138ad8-eb2f-4c7c-aef7-90482a67c45c Total devices 3 FS bytes used 768.00KiB devid 1 size 5.00GiB used 1.52GiB path /dev/xvdb devid 2 size 5.00GiB used 520.00MiB path /dev/xvdc devid 3 size 5.00GiB used 1.51GiB path /dev/xvdd For some reason one disk is faulty and needs to be replaced. # btrfs filesystem show Label: 'MYBTRFS' uuid: … [Read more...] about How to Replace a Failed Btrfs Device
How to Check Btrfs FileSystem Usage and Perform Balancing
In Btrfs file system there are chunks that are allocated for regular data, metadata. There are also chunks that are allocated to store file system information and also about where other chunks are located on the physical disk. Those chunks can only store the data. Very occasionally, a chunk type may fill up and start to run out of space. However, there may (and often is) still space available in other chunks. Therefore, some space needs to be freed up on it. There is a balancing feature … [Read more...] about How to Check Btrfs FileSystem Usage and Perform Balancing
How to Re-Balance BTRFS to Free Disk Space
The Problem The BTRFS filesystem has filled on the server, and thus some space needs to be freed up on it. There is a re-balancing feature available in btrfs. The primary purpose of the re-balance feature is to spread block groups across all devices so they match constraints defined by the respective profiles and this is done when btrfs need re-balancing to fix issues with chunks being unbalanced. The Solution It is common for a btrfs device to fill up due to the fact that it does not … [Read more...] about How to Re-Balance BTRFS to Free Disk Space
BTRFS: too many missing devices, writeable mount is not allowed
The Problem Assembling a BTRFS device during boot fails with error BTRFS: too many missing devices, writeable mount is not allowed The disks have been mistakenly deleted The Solution The missing disks in the raid array do not allow the filesystem to be mounted. Below are the logs from dmesg: [ 44.706956] btrfs: disk space caching is enabled [ 44.708006] btrfs: failed to read the system array on sdd1 [ 44.721272] btrfs: open_ctree failed [ 45.437152] nr_pdflush_threads exported in … [Read more...] about BTRFS: too many missing devices, writeable mount is not allowed
Command ‘df -i’ Shows ‘Inode=0’ on BTRFS File System
The Problem On a BTRFS file system, the df command shows that the total number of inodes is 0. The Used and Free numbers are 0. # df -i / Filesystem Inodes IUsed IFree IUse% Mounted on /dev/xvda2 0 0 0 - / Note: The above output is taken from a virtual machine. The Solution BTRFS does not use inodes in quite the same way as other filesystems, and it has no pre-determined limits, so it has nothing to count. The inode counts for BTRFS will always show … [Read more...] about Command ‘df -i’ Shows ‘Inode=0’ on BTRFS File System
rm: cannot remove ‘doc/by-app’: Function not implemented (CentOS/RHEL 7)
The Problem Some user directories cannot be deleted. For example: /root/.cache/doc/ directory /root/.cache/doc/by-app directory If we try to delete the directory, we get the below error: # rm -rf /root/.cache/doc/ rm: cannot remove 'doc/by-app': Function not implemented The Solution The directories are the mount points for /dev/fuse device. # mount --mount (ext, ocfs2, nfs, gfs, fuse, cifs, btrfs, xfs) /dev/fuse on /root/.cache/doc type fuse … [Read more...] about rm: cannot remove ‘doc/by-app’: Function not implemented (CentOS/RHEL 7)
How To Change Pacemaker Cluster Heartbeat Timeout In CentOS/RHEL 7
Question: How to change pacemaker cluster heartbeat timeout in CentOS/RHEL 7? By default, the heartbeat of pacemaker in CentOS/RHEL 7 is set to 1000(ms), you could increase it by the below steps. 1. Appending/Chaning the token to the totem section in the corosync config file /etc/corosync/corosync.conf. # cat /etc/corosync/corosync.conf totem { version: 2 cluster_name: pcmk secauth: off transport: udpu token: 10000 … [Read more...] about How To Change Pacemaker Cluster Heartbeat Timeout In CentOS/RHEL 7
SSH Login Stuck At : “debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP” CentOS/RHEL 7
The Problem Trying to login via SSH, the session hangs. Adding "-vvv" option, shows that it hangs with below messages: debug1: expecting SSH2_MSG_KEX_ECDH_REPLY The Solution MTU was set to 9000 : # ip add| grep -i eth0 2: eth0: mtu 9000 qdisc pfifo_fast state UP group default qlen 1000 inet x.x.x.x/24 brd x.x.x.x scope global noprefixroute eth0 Tcpdump captured for both nodes shows that a packet whose length is greater than 1500 was being retransmitted. 5 11:13:10.261757 x.x.x.x … [Read more...] about SSH Login Stuck At : “debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP” CentOS/RHEL 7
How To Find When The Spfile Was Created On Linux Server
Question: The user needs to know when was the last time spfile was created or modified on a Linux server. How this can be found out? Use the below approach to get the creation time of spfile. 1. Find the inode of the file using the 'ls -i' command: $ ls -i spfile[SID].ora 3950836 spfile[SID].ora Here 3950836 is the inode number of the spfile. 2. Find the root/parent filesystem that our file resides in. $ cd $ORACLE_HOME/dbs $ df -h . Filesystem Size Used Avail Use% Mounted … [Read more...] about How To Find When The Spfile Was Created On Linux Server