Basics

Formatting and Mounting a new drive in Linux

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I have installed a new slave hard drive. How do I format it and mount it?

Solution:

1. Login as root: and type the following command:

[root@34 root]# fdisk /dev/hdc

2. This screen will appear:

The number of cylinders for this disk is set to 10011.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)

3. Press p for print, this will show you the current partitons on the drive:

Command (m for help): p

Disk /dev/hdc: 82.3 GB, 82348277760 bytes
255 heads, 63 sectors/track, 10011 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System

4. There are no current partitions, if there were, press d to delete them. Then press n to create a new partition and follow the rest of the commands:

Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-10011, default 1): Enter
Using default value 1: Enter
Last cylinder or +size or +sizeM or +sizeK (1-10011, default 10011): Enter
Using default value 10011

5: Write your new partiton to the drive:

Command (m for help): w
The partition table has been altered!

—————————————

6. Now to make the file system.

[root@34 root]# mkfs.ext3 /dev/hdc1
mke2fs 1.32 (09-Nov-2002)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
10059776 inodes, 20103331 blocks
1005166 blocks (5.00%) reserved for the super user
First data block=0
614 block groups
32768 blocks per group, 32768 fragments per group
16384 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424

—————————————–

7. Now to make a directory to mount the new drive to.

[root@34 root]# mkdir /backups
[root@34 root]# mount /dev/hdc1 /backups
[root@34 root]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/hda3 75G 1.3G 70G 2% /
/dev/hda1 99M 14M 81M 15% /boot
none 243M 0 243M 0% /dev/shm
/dev/hdc1 76G 33M 72G 1% /backups

You will see that the new drive is labled /dev/hdc1 and is mounted to /backups.
——————————————-

8. Now edit the /etc/fstab so that the mount is there after a reboot.

Current fstab is shown below:

LABEL=/ / ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
none /dev/pts devpts gid=5,mode=620 0 0
none /proc proc defaults 0 0
none /dev/shm tmpfs defaults 0 0
/dev/hda2 swap swap defaults 0 0

9. Now we are going to add one line at the end:

[root@34 root]# vi /etc/fstab
LABEL=/ / ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
none /dev/pts devpts gid=5,mode=620 0 0
none /proc proc defaults 0 0
none /dev/shm tmpfs defaults 0 0
/dev/hda2 swap swap defaults 0 0
/dev/hdc1 /backups ext3 defaults 0 0

Save and quit vi.

rndc: the key is invalid

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Problem:

———
Issue:
———
While starting named, or when running /etc/rc.d/init.d/named status, you get the following error:
rndc: connection to remote host closed This may indicate that the remote server is using an older version of the command protocol, this host is not authorized to connect, or the key is invalid.

Solution:

——-
Fix:
——-

Run rndc-confgen.
running rndc-confgen would ouput something like this:
# Start of rndc.conf
key “rndc-key” {
algorithm hmac-md5;
secret “lYzcmf255w8BC6PHTSYCQA==”;
};

options {
default-key “rndc-key”;
default-server 127.0.0.1;
default-port 953;
};
# End of rndc.conf

# Use with the following in named.conf, adjusting the allow list as needed:
# key “rndc-key” {
# algorithm hmac-md5;
# secret “lYzcmf255w8BC6PHTSYCQA==”;
# };
#
# controls {
# inet 127.0.0.1 port 953
# allow { 127.0.0.1; } keys { “rndc-key”; };
# };
# End of named.conf

do as mentioned in the output, that is, copy the rndc.conf part to /etc/rndc.conf (of course, remove all the existing entries)
in /etc/named.conf, remove the existing key and controls section, and paste the one from the output of rndc-confgen.
restart named (/etc/rc.d/init.d/named restart).
This fixes the issue

semget: No space left on device

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This relates to semaphores on your system (you’ve run out). Run the following to clear them out:

ipcs | grep apache | awk ‘{print $2}’ > sem.txt
for i in `cat sem.txt`; do { ipcrm -s $i; }; done;

For cPanel servers :

ipcs | grep nobody | awk ‘{print $2}’ > sem.txt
for i in `cat sem.txt`; do { ipcrm -s $i; }; done;

 

Finally restart Apache :

/etc/init.d/httpd restart

Or 
service httpd restart

 

 

What is /dev/shm and its practical usage ?

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What is /dev/shm and its practical usage ?

/dev/shm is nothing but implementation of traditional shared memory concept. It is an efficient means of passing data between programs. One program will create a memory portion, which other processes (if permitted) can access. This will result into speeding up things on Linux.

If you type mount command you will see /dev/shm as a tempfs file system. Therefore, it is a file system, which keeps all files in virtual memory. Everything in tmpfs is temporary in the sense that no files will be created on your hard drive. If you unmount a tmpfs instance, everything stored therein is lost. By default almost all distro configured to use /dev/shm.

Nevertheless, where can I use /dev/shm?
You can use /dev/shm to improve the performance of application software or overall Linux system performance. On heavily loaded system, it can make tons of difference. For example VMware workstation/server can be optimized to improve your Linux host’s performance (i.e. improve the performance of your virtual machines).

For example, if you have 8GB RAM then remount /dev/shm as follows:

# mount -o remount,size=8G /dev/shm

To be frank if you have more than 2GB RAM and if you running multiple Virtual machines this hack always improves performance.

Fatal error: Allowed memory size of 123456 bytes exhausted (tried to allocate 234567 bytes) in /path/file.php

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Php is setup is to limit memory usage per process. If you require more, this limit can be increased.
Edit

/usr/local/lib/php.ini

If you are unsure about the php.ini path, You can find your server php.ini using command :

php -i | grep php.ini

Configuration File (php.ini) Path => /usr/local/lib

Loaded Configuration File => /usr/local/lib/php.ini

and set:

memory_limit = 8M ; Maximum amount of memory a script may consume (8MB)

to a higher value, like 20M. Save, exit, then restart apache.