Notes and Stuff
A logical volume provides storage virtualization so you are not restricted to physical disks sizes. The hardware storage configuration is hidden and the logical volume can be resized and moved on the fly.
An LVM Logical Volume has three components:
First of all, you have to initialize a new PV using the pvcreate command:
pvcreate /dev/sdc*
You can create a PV from a whole disk rather than partitions.
To send a request using curl via proxy:
$ curl -v --proxy [proxy_address]:[port] [protocol://][hostname]
Sometimes when you add new storage to a running VM you won’t see it; the SCSI bus needs to be re-scanned to make the new disk visible.
echo "---" > /sys/class/scsi_host/hostX/scan
X is the number of the SCSI host to scan."---" tells the SCSI host to rescan all controllers, channels and LUNs.
To force a re-sync of the kernel for all the SCSI devices:
echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescanwhere 0:0:0:0 is the device you want to sync.
If you increased the size of an existing disk but you are not able to see the new disk size:
echo "1" > /sys/class/block/sdX/device/rescan
"1" is a flag that will trigger re-scan on the SCSI host.
Check why the service is in Maintenance State:
svcs -x FMRI
Check if there’s any process dependent to the service and kill them (optional):
svcs -p FMRI
pkill -9 process-name
Finally, restore the service:
svcadm clear FMRI
Here’s a Bash script to check software RAID that will send an e-mail reporting the array status:
#!/bin/bash
# check_raid.sh
EMAIL="your@email.com"
if egrep "\[.*_.*\]" /proc/mdstat > /dev/null
then
logger -s "mdcheck: RAID devices ERROR"
echo "Software RAID devices ERROR on ${HOSTNAME}" | /bin/mail -s \
"$0: Software RAID devices ERROR on ${HOSTNAME}" ${EMAIL}
else
logger -s "mdcheck: RAID devices OK"
echo "Software RAID devices OK on ${HOSTNAME}" | /bin/mail -s \
"$0: Software RAID device OK on ${HOSTNAME}" ${EMAIL}
fi
If you’re looking for a specific value:
awk '$2==1 {print $3}' file
If you’re looking for a string, you have to use quotes otherwise awk will assume it’s a variable name:
awk '$1 == "findtext" {print $3}' file
OpenSSH is the de facto standard implementation of the SSH protocol.
If you use ssh-keygen with the default options, it will generate a private and a public key that will work with virtually any server.
Unfortunately, out there are Windows users that bother Linux admins with .ppk key generated by PuTTY; both keys are stored in this single proprietary file.
You can convert this file and obtain standard OpenSSH key pairs using puttygen provided with the putty package available on many distros.
puttygen your_key.ppk -O [output-type] -o [output-file]
output-type refers to they key type, private-openssh or public-openssh.
I had to update a couple of NTP servers and after rebooting Nagios was returning an alert on the check_ntp_peer check, indicating a time drift.
To fix it, I forced a clock update with NTP servers:
systemctl stop ntpd
ntpdate -s ntp1.inrim.it
systemctl start ntpd