Symetric encryption is an encryption that uses same key to decrypt.
here is a way to encrypt file with symetric key without user interact ( batch )
gpg --batch -q --passphrase '<password>' --cipher-algo AES256 -c <file>
Create TAP/TUN device CentOS 7
Here is how to do it on CentOS 7 / RedHat 7 where the command tunctl is missing
and when you try to run ifconfig you get an error
~# ifconfig tap0 10.0.0.1/30
SIOCSIFADDR: No such device
tap0: ERROR while getting interface flags: No such device
SIOCSIFNETMASK: No such device
to solve this you may run this commands
1. first we must create the device using ip command
# ip tuntap add tap0 mode tap
2. run ifconfig
~# ifconfig tap0 10.0.0.1/30 ~# ifconfig tap0 tap0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 10.0.0.1 netmask 255.255.255.252 broadcast 10.0.0.3 ether 32:f5:3a:44:a5:64 txqueuelen 500 (Ethernet) RX packets 0 bytes 0 (0.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 0 bytes 0 (0.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Bash Special Variables
Bash shell has some built in variables that can be use in scripts
for example if you want to know the process id of the current command , you may use $$
here is a list of some special variables
| $# | Number of command-line arguments. |
| $_ | The underscore variable is set at shell startup and contains the absolute file name of the shell or script being executed as passed in the argument list. Subsequently, it expands to the last argument to the previous command, after expansion. It is also set to the full pathname of each command executed and placed in the environment exported to that command. When checking mail, this parameter holds the name of the mail file. |
| $- | A hyphen expands to the current option flags as specified upon invocation, by the set built-in command, or those set by the shell itself (such as the -i). |
| $? | Exit value of last executed command. |
| $ | Process number of the shell. |
| $! | Process number of last background command. |
| $0 | First word; that is, the command name. This will have the full pathname if it was found via a PATH search. |
| $n | Individual arguments on command line (positional parameters). The Bourne shell allows only nine parameters to be referenced directly (n = 1–9); Bash allows n to be greater than 9 if specified as ${n}. |
| $*, $@ | All arguments on command line ($1 $2 …). |
| “$*” | All arguments on command line as one string (“$1 $2…”). The values are separated by the first character in $IFS. |
| “$@” | All arguments on command line, individually quoted (“$1” “$2” …). |
simple install sun java
a quick and eazy way to install java under linux
1. download jre or jdk from www.java.com
2. create a directory to hold the versions
# mkdir /usr/java
3. extract the tar file under the directory
# tar -xzvf jre-7u45-linux-x64.tar.gz -C /usr/java # ln -s /usr/java/jre1.7.0_45 /usr/java/jre-latest
4. the last part is to create links in the system in order to
make sure it uses this new java version we just extracted .
* global java command
debian linux based version:
# update-alternatives --install /usr/bin/java java /usr/java/jre-latest/bin/java 90 # update-alternatives --config java
RedHat linux based version :
# alternatives --install /usr/bin/java java /usr/java/jre-latest/bin/java 90 alternatives --config java
browsers links
ln -s /usr/java/jre-latest/lib/amd64/libnpjp2.so <path to install dir>/plugins/
bash history security
Bash history can reviel what a person commands where .
but what if the person wants to hide his tracks , he may use the
unset HISTFILE
will couse bash to delete the history upon logout .
there is how ever a harden attribute you may set to overcome this problem
when a user login , there are set of files/scripts the profile runs .
one place you may put such script would be under /etc/profile.d/ , with file extension sh
as it is being called by /etc/profile .
just place this small line in there :
readonly HISTFILE
now when a person wants to unset this parameter , bash will scream with this error
-su: unset: HISTFILE: cannot unset: readonly variable
Move ASM disk across storage online
This is a way you can use to copy/move your ASM disks to new location
without the need to stop your instance. it include command to be run
by root and by asm admin
1. creating the new disks(LUN) as ASM devices (run as root)
[[email protected] ~]# /etc/init.d/oracleasm listdisks DATA1 OCR1 [[email protected] ~]# /etc/init.d/oracleasm createdisk DATA2 /dev/sdb8 Marking disk "DATA2" as an ASM disk: [ OK ] [[email protected] ~]# [[email protected] ~]# /etc/init.d/oracleasm listdisks DATA1 DATA2 OCR1
2. List disk in disk-group (run as asmadmin)
SQL> select GROUP_NUMBER,NAME,STATE,TOTAL_MB from v$asm_diskgroup ; GROUP_NUMBER NAME STATE TOTAL_MB ------------ ------------------------------ ----------- ---------- 1 OCR MOUNTED 964 2 DATA MOUNTED 4777 SQL> select NAME,GROUP_NUMBER,REDUNDANCY from v$asm_disk ; NAME GROUP_NUMBER REDUNDA ------------------------------ ------------ ------- 0 UNKNOWN DATA1 2 UNKNOWN OCR1 1 UNKNOWN
3. Adding disk to DATA disk-group (run as asdmadmin)
SQL> ALTER DISKGROUP DATA REBALANCE POWER 0 ; Diskgroup altered. SQL> ALTER DISKGROUP DATA ADD DISK 'ORCL:DATA2' NAME DATA2 ; Diskgroup altered. SQL> ALTER DISKGROUP DATA DROP DISK DATA1 ; Diskgroup altered. SQL> ALTER DISKGROUP data REBALANCE POWER 1; Diskgroup altered. SQL> select NAME,GROUP_NUMBER,REDUNDANCY from v$asm_disk ; NAME GROUP_NUMBER REDUNDA ------------------------------ ------------ ------- 0 UNKNOWN DATA1 1 UNKNOWN DATA2 1 UNKNOWN OCR1
Note that DATA1 was marked as DROP , it will stop showing once all data sync to DATA2
the process can be monitored by this query (run as asmadmin)
SELECT g.name "Diskgroup", 100*(max((d.total_mb-d.free_mb)/d.total_mb)-min((d.total_mb-d.free_mb)/d.total_mb))/max((d.total_mb-d.free_mb)/d.total_mb) "Imbalance", 100*(max(d.total_mb)-min(d.total_mb))/max(d.total_mb) "Variance", 100*(min(d.free_mb/d.total_mb)) "MinFree", count(*) "DiskCnt", g.type "Type" FROM v$asm_disk d, v$asm_diskgroup g WHERE d.group_number = g.group_number and --d.group_number = 1 and d.state = 'NORMAL' and d.mount_status = 'CACHED' 12 GROUP BY g.name, g.type; Diskgroup Imbalance Variance MinFree ------------------------------ ---------- ---------- ---------- ---------- Type ------ OCR EXTERN DATA EXTERN • DiskCnt 0 63.3817427 1 0 59.5143395 1
Manage partitions on a raw device file
Every once in a while there comes a time when you need to use a file as raw device
for example when using qemu qcow file or if you want to have your home directory portable and encrypted
in this example i am using one file named my-hd-image.file and 2 Linux partitions inside it . lets start
Creating the raw device file is simply by using dd ( can also be use via qemu-img )
dd if=/dev/zero of=my-hd-image.file bs=1M count=1024
Create partitions inside the new disk using fdisk , in my file
I had created 2 partitions of 512M
Device Boot Start End Blocks Id System my-hd-image.file1 2048 1050623 524288 83 Linux my-hd-image.file2 1050624 2097151 523264 83 Linux
creating the file system using loop devices to be linked to specific offset inside the file
so that each partition will have its own loop device . the offset calculation is in bits
and i am using bc to calculate it fast for me . the offset of each partition is its start block times 512
witch is the block size ( unless you have set a different one upon creation )
Partition my-hd-image.file1 starts at offset 2048
echo "2048 * 512" | bc 1048576
Partition my-hd-image.file2 starts at offset 1050624
echo "1050624 * 512" | bc 537919488
use the calculation offset to map to the loop device
losetup -o 1048576 /dev/loop1 my-hd-image.file losetup -o 537919488 /dev/loop2 my-hd-image.file
Now we can format the partition
mkfs.ext4 /dev/loop1 mkfs.ext4 /dev/loop2
all is left to do is mount the partitions
root@# mkdir /mnt/my-hd-partition-1 root@# mkdir /mnt/my-hd-partition-2 root@# mount /dev/loop1 /mnt/my-hd-partition-1 root@# mount /dev/loop2 /mnt/my-hd-partition-2
To remove the device just use unmount and to release the loop device
you will need to use losetup
umount /mnt/my-hd-partition-2 umount /mnt/my-hd-partition-1 losetup -d /dev/loop1 losetup -d /dev/loop2
multi-line comment with vi
Vi editor is one of my favourite text editor to work with under linux/Unix systems ,
and from time to time there comes a need to mark multiple lines as comment .
here is how you can do it in vi/vim :
1. using Ctrl+v (visual block) mark the lines you wish to comment
2. go into insert mode Shift+i then write the comment (could be anything actually )
3. finished by clicking the Esc button .
and vwalla you lines are now marked as comment
to remove multi-line comment ,simply go through the same steps but
after marking the lines just press d for delete or c for clean
oracleasm cant find disks
When installing grid under Oracle Linux/RedHat , the grid installer may fail to see the asm disks
even if we just install the software , the asmca may also fail to see the disks .
in order to fix it , we just need to set the scanning path to where the disks are
/dev/oracleasm/disks/*
and now the installer can see the disks
samba PDC sambaLogonTime update
Samba doesnt update sambaLogonTime in LDAP when a user login
in order to have it set , one can run a script that will do it
set up a script /root/update_sambaLogonTime.sh
#!/bin/bash TIMESTAMP=$(date +%s) ldapmodify -x -h localhost -D "cn=Manager,dc=example,dc=com" -y /root/pass-test <<EOF dn: uid=$1,ou=People,dc=example,dc=com changetype: modify replace: sambaLogonTime sambaLogonTime: $TIMESTAMP EOF
now create a pass-test file by running echo with “-n” in order to remove the newline “n”
because ldapmodify doesnt not chop it
echo -n "mypassword" > /root/pass-test
now just add a line under [netlogon] in smb.conf
root preexec = /root/update_sambaLogonTime.sh "%u"