CentOS 7 如何更新 php 版本

 之前利用 Remi 的 Repo 來安裝 php 7.0，現在想把 7.0 更新到 7.4，又不想裝上每個套件都加上後綴 xxx74 這種醜醜的名稱，這時候可以透過修改 Remi 的 Repo 來達成。

# yum-config-manager  --enable remi-php74

# yum update

二行指令，搞定！

Ubuntu Server 18.04 更新到 20.04.1 後，Xshell4 無法連線(no matching key exchange)

 前兩天把 Ubuntu Server 18.04 升級成 20.04.1，結果，發生用 Xshell 4 無法連線，出現「no matching key exchange 」，用 putty 連線也一樣。

查了 putty 的版本，是0.6x 的版本，重新下載新版 (0.74)後，putty 就可以正常連線了。不過， 我用另一台電腦上的 Xshell 6 其實也可以連線，所以，但是因為某個原因，我並不想把 Xshell4 升級，所以又努力查原因…

看了一下 log 檔：

no matching key exchange method found. Their offer: diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

看來應該是某個(些)運算法不支援了，若要強制支援的話，得另外在 「/etc/ssh/sshd_config」加上參數：

KexAlgorithms diffie-hellman-group1-sha1,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group1-sha1,curve25519-sha256@libssh.org

把 sshd 重新啟動後，Bingo!!! 連線正常。

Ref: xshell4連接ubuntu，報錯No matching outgoing encryption

[轉貼] How To Install Linux, Nginx, MySQL, PHP (LEMP stack) on Ubuntu 20.04

文章來源： https://www.digitalocean.com/community/tutorials/how-to-install-linux-nginx-mysql-php-lemp-stack-on-ubuntu-20-04

轉: How to enable and start services on Alpine Linux

Alpine Linux 是個小巧輕量的 Linux系統，非常值得試試

原文：https://www.cyberciti.biz/faq/how-to-enable-and-start-services-on-alpine-linux/

How do I add or delete service at boot time on an Alpine Linux? How do I enable service such as Nginx/Apache at boot time on an Alpine Linux? How do I start/stop/restart services on an Alpine Linux?
Alpine Linux comes with OpenRC init system. This tutorial shows how to use the various command on OpenRC to manage services.View status of all services
Type the following command:# rc-status

[Linux] deepin linux 安裝 k3b後無法燒錄

因為權限不足的的關係，所以燒錄音樂光碟後，無法燒錄，查了一下資料後，執行下列指令後，有解。

sudo chmod 4711 /usr/bin/wodim; sudo chmod 4711 /usr/bin/cdrdao

延伸閱讀：鳥哥的Linux 私房菜-- 檔案與目錄管理

systemd 和 upstart 啟用和停用

參考： https://askubuntu.com/questions/19320/how-to-enable-or-disable-services
-----------------------------------------------------------------------------------------------------------------------

Temporary enabling/disabling services

To stop and start services temporarily (Does not enable / disable them for future boots), you can type service SERVICE_NAME. For example:

• sudo service apache2 stop (Will STOP the Apache service until Reboot or until you start it again).
• sudo service apache2 start (Will START the Apache service assuming it was stopped before.).
• service apache2 status (Will tell you the STATUS of the service, if it is either enabled/running of disabled/NOT running.).
• sudo service apache2 restart (Will RESTART the service. This is most commonly used when you have changed, a config file. In this case, if you changed either a PHP configuration or an Apache configuration. Restart will save you from having to stop/start with 2 command lines)
• service apache2 (In this case, since you did not mention the ACTION to execute for the service, it will show you all options available for that specific service.) This aspect varies depending on the service, for example, with MySQL it would only mention that it is missing a parameter. For other services like networking service it would mention the small list of all options available.

---

SYSTEMD

Starting with Ubuntu 15.04, Upstart will be deprecated in favor of Systemd. With Systemd to manage the services we can do the following:

systemctl start SERVICE - Use it to start a service. Does not persist after reboot

systemctl stop SERVICE - Use it to stop a service. Does not persist after reboot

systemctl restart SERVICE - Use it to restart a service

systemctl reload SERVICE - If the service supports it, it will reload the config files related to it without interrupting any process that is using the service.

systemctl status SERVICE - Shows the status of a service. Tells whether a service is currently running.

systemctl enable SERVICE - Turns the service on, on the next reboot or on the next start event. It persists after reboot.

systemctl disable SERVICE - Turns the service off on the next reboot or on the next stop event. It persists after reboot.

systemctl is-enabled SERVICE - Check if a service is currently configured to start or not on the next reboot.

systemctl is-active SERVICE - Check if a service is currently active.

systemctl show SERVICE - Show all the information about the service.

sudo systemctl mask SERVICE - Completely disable a service by linking it to /dev/null; you cannot start the service manually or enable the service.

sudo systemctl unmask SERVICE - Removes the link to /dev/null and restores the ability to enable and or manually start the service.

---

UPSTART (Deprecated Since 15.04)

If we want to use the official Upstart way (Note that, for the moment, not all services have been converted to Upstart), we could use the following commands:

status SERVICE - This will tell us if a converted service is running or not. Note that this is deprecated in favor of start, stop, status & restart. It will also tell us if a service has not yet been converted to upstart:

A converted service would typically output the current status (Starting, Running, Stopping...) and process ID. A non converted service would give an error about an unknown job.

Some shortcuts may only work with the service command above but not with the commands below unless they are 100% converted to upstart services:

• START - sudo start mysql
• STOP - sudo stop mysql
• RESTART - sudo restart mysql
• STATUS - sudo status smbd

Enabling / Disabling a service

To toggle a service from starting or stopping permanently you would need to:

echo manual | sudo tee /etc/init/SERVICE.override

where the stanza manual will stop Upstart from automatically loading the service on next boot. Any service with the .override ending will take precedence over the original service file. You will only be able to start the service manually afterwards. If you do not want this then simply delete the .override. For example:

echo manual | sudo tee /etc/init/mysql.override

Will put the MySQL service into manual mode. If you do not want this, afterwards you can simply do

sudo rm /etc/init/mysql.override

and Reboot for the service to start automatically again. Of course to enable a service, the most common way is by installing it. If you install Apache, Nginx, MySQL or others, they automatically start upon finishing installation and will start every time the computer boots. Disabling, as mentioned above, will make use of the service manual.

嗯！莫名踩雷了 mariadb-server

利用 MariaDb 架 nextcloud 平台，收集校務評鑑資料，一開始裝好了之後，用起來都很正常。

但是安全更新後把伺服器重新開機，就發現nextcloud 掛了，遠端登入後才發現是資料庫沒啟動，立馬手動執行

sudo systemctl restart mysqld.server

結果等了許多，跳出了另一個錯誤訊息

2018-05-29 13:46:04 139927905056960 [Note] Using unique option prefix 'myisam-recover' is error-prone and can break in the future. Please use the full name 'myisam-recover-options' instead.
2018-05-29 13:46:04 139927905056960 [Note] Using unique option prefix 'myisam-recover' is error-prone and can break in the future. Please use the full name 'myisam-recover-options' instead.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Uses event mutexes
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Compressed tables use zlib 1.2.8
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Using Linux native AIO
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Number of pools: 1
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Using SSE2 crc32 instructions
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Completed initialization of buffer pool
2018-05-29 13:46:04 139927257839360 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: The first innodb_system data file 'ibdata1' did not exist. A new tablespace will be created!
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Setting file './ibdata1' size to 12 MB. Physically writing the file full; Please wait ...
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: File './ibdata1' size is now 12 MB.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Setting log file ./ib_logfile101 size to 50331648 bytes
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Setting log file ./ib_logfile1 size to 50331648 bytes
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: New log files created, LSN=45790
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Doublewrite buffer not found: creating new
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Doublewrite buffer created
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: 128 out of 128 rollback segments are active.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Creating foreign key constraint system tables.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Creating tablespace and datafile system tables.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Creating sys_virtual system tables.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Creating shared tablespace for temporary tables
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: Waiting for purge to start
2018-05-29 13:46:04 139927905056960 [Note] InnoDB: 5.7.22 started; log sequence number 0
2018-05-29 13:46:04 139927905056960 [Note] Plugin 'FEEDBACK' is disabled.
2018-05-29 13:46:04 139927905056960 [ERROR] Could not open mysql.plugin table. Some plugins may be not loaded
2018-05-29 13:46:04 139927905056960 [ERROR] Can't open and lock privilege tables: Table 'mysql.servers' doesn't exist
2018-05-29 13:46:04 139927905056960 [Note] Server socket created on IP: '127.0.0.1'.
2018-05-29 13:46:04 139927905056960 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.user' doesn't exist

本來以為是資料庫故障了，結果切換到 /var/lib/mysql 後，發現資料庫、資料表似乎都在，疑問之下，開啟  /var/log/syslog ，發現又一串錯誤訊息…

May 30 20:15:45 ubuntu systemd[1]: Starting MariaDB 10.2.15 database server...
May 30 20:15:46 ubuntu kernel: [97757.266462] audit: type=1400 audit(1527682546.054:13): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/12073/status" pid=12073 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=106 ouid=106
May 30 20:15:46 ubuntu kernel: [97757.266776] audit: type=1400 audit(1527682546.054:14): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/sys/devices/system/node/" pid=12073 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=106 ouid=0
May 30 20:15:46 ubuntu kernel: [97757.267025] audit: type=1400 audit(1527682546.054:15): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/proc/12073/status" pid=12073 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=106 ouid=106
May 30 20:15:46 ubuntu kernel: [97757.357815] audit: type=1400 audit(1527682546.142:16): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/etc/mysql/mariadb.conf.d/" pid=12073 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=106 ouid=0
May 30 20:15:46 ubuntu mysqld[12073]: #007/usr/sbin/mysqld: Can't read dir of '/etc/mysql/mariadb.conf.d/' (Errcode: 13 "Permission denied")
May 30 20:15:46 ubuntu mysqld[12073]: #007/usr/sbin/mysqld: Can't read dir of '/etc/mysql/mariadb.conf.d/' (Errcode: 13 "Permission denied")
May 30 20:15:46 ubuntu mysqld[12073]: Fatal error in defaults handling. Program aborted
May 30 20:15:46 ubuntu kernel: [97757.360216] audit: type=1400 audit(1527682546.146:17): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/etc/mysql/mariadb.conf.d/" pid=12073 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=106 ouid=0
May 30 20:15:46 ubuntu systemd[1]: mariadb.service: Main process exited, code=exited, status=1/FAILURE
May 30 20:15:46 ubuntu systemd[1]: Failed to start MariaDB 10.2.15 database server.
May 30 20:15:46 ubuntu systemd[1]: mariadb.service: Unit entered failed state.
May 30 20:15:46 ubuntu systemd[1]: mariadb.service: Failed with result 'exit-code'.

本來以為是 DB 設定檔出了問題，也懷疑過 mariadb-common 和 mysql-common 這 2 個系統自己裝進來的套件，混在一起後有衝突，調整了許久還是無法啟動。

後來再仔細看了一下 log 內容，似乎是被 denied ，permission 不夠，苦搜了許久，終於把這雷也掃了，結論：

編輯   /etc/apparmor.d/usr.sbin.mysqld，增加下列內容，重新啟動服務後，正常！呼！

/etc/mysql/*.cnf r,
/{,var/}run/mysqld/mysqld.pid w,
/{,var/}run/mysqld/mysqld.sock w,
/usr/lib/mysql/plugin/ r,
/proc/*/status r,
/sys/devices/system/node/ r,
/sys/devices/system/node/node0/meminfo r,
/run/systemd/notify w,

Deepin / Debian ppa list

SMplayer (參考網址)

 for Debian 8

wget -nv https://download.opensuse.org/repositories/home:smplayerdev/Debian_8.0/Release.key -O Release.key
apt-key add - < Release.key
apt-get update
echo 'deb http://download.opensuse.org/repositories/home:/smplayerdev/Debian_8.0/ /' > /etc/apt/sources.list.d/home:smplayerdev.list
apt-get update
apt-get install smplayer

Visual Studio Code (參考網址)

curl https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > microsoft.gpg
sudo mv microsoft.gpg /etc/apt/trusted.gpg.d/microsoft.gpg
sudo sh -c 'echo "deb [arch=amd64] https://packages.microsoft.com/repos/vscode stable main" > /etc/apt/sources.list.d/vscode.list'
sudo apt-get update
sudo apt-get install code

 megaSync (參考網址)

echo deb http://mega.co.nz/linux/MEGAsync/Debian_8.0/ ./ | sudo tee /etc/apt/sources.list.d/megasync.list
wget https://mega.co.nz/linux/MEGAsync/Debian_8.0/Release.key && sudo apt-key add Release.key
sudo apt update
sudo apt install megasync

Nodejs(參考網址) 

Node.js v10.x:

# Using Ubuntu
curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
sudo apt-get install -y nodejs

# Using Debian, as root
curl -sL https://deb.nodesource.com/setup_10.x | bash -
apt-get install -y nodejs

Node.js v8.x:

# Using Ubuntu
curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -
sudo apt-get install -y nodejs

# Using Debian, as root
curl -sL https://deb.nodesource.com/setup_8.x | bash -
apt-get install -y nodejs

lftp 下載／上傳整個目錄

lftp 比 ftp 方便多了，特別當需要上傳或下載整個目錄時，特別方便。

下載整個目錄   mirror  <dir_name>

上傳整個目錄   mirror  -R  <local_dir_name>

lftp 連上後無法顯示目錄檔案

在 Ubuntu 16.04 上安裝  lftp 程式，連上 ftp 站台後無法顯示目錄檔案。
出現的錯誤訊息為：

Fatal error: Certificate verification: Not trusted

解決方法為：
編輯  /etc/lftp.conf 檔案
在檔案結尾加上 下列指令，重新連上就可以正常顯示了。

set ssl:verify-certificate no

[Ubuntu] Google Chromecast 突然無法在chrome 瀏覽器上播放

適用 chrome 55 以後版本

• 在網址列上輸入 「chrome://flags/#media-router」
• 將 「Default」 改為 「Disable」
• 重新啟動  Google Chrome

[轉] How to Install Arch Linux [Step by Step Guide]

文章出處：https://itsfoss.com/install-arch-linux/

整理步驟大致如下：詳文請至文章出處瀏覽
Step 1: Download the ISO
Step 2: Create a live USB of Arch Linux
Step 3: Boot from the live USB
Step 4: Partitioning the disks
Step 5: Creating filesystem
Step 6: Installation
Step 7: Configuring the system
Step 8. Setting Timezone
Step 9. Setting up Locale.
Step 10. Installing bootloader, setting up hostname and root password
Step 11: Install a desktop environment (GNOME in this case)

[Ubuntu] 單網卡多個IP

1. 臨時性

sudo ip address add <ip-address>/<netmask> dev <interface>

例：

sudo ip address add 10.231.141.231/24 dev eth0

2. 永久性 /etc/network/interfaces

iface eth0 dhcp
iface eth0 inet static
    address 10.231.141.231/24
iface eth0 inet static
    address 10.241.141.231/24

重新啟動

sudo ifdown eth0 && sudo ifup eth0

補充：The iproute2 suite:

The iproute2 suite is the communication suite for interprocess communication beween the kernel and the user space via the netlink protocol. It should replace the whole standard network tools. Here is what they replace:

• ifconfig --> ip addr and ip link
• route --> ip route
• arp --> ip neigh
• iptunnel --> ip tunnel
• ipmaddr --> ip maddr
• netstat --> ss

[linux] 轉：語系設定 locale

講解的很清楚，值得看！

參考網址：https://moto.debian.tw/viewtopic.php?t=6213

[Linux] RHEL 6 vs. 7

新的學校首頁系統即將更換，Linux 系統會提供 CentOS的虛擬機；先來熟悉一下 Redhat 系的操作。
看起來 RHEL 6 比較接近 Ubuntu 14.04，RHEL 7則接近 Ubuntu 16.04，

Ref:

1. https://arkit.co.in/rhel-6-vs-rhel-7-difference-previous-newer-version/
2. http://simplylinuxfaq.blogspot.tw/p/major-difference-between-rhel-7-and-6.html

Feature Name	RHEL 6	RHEL 7
Default File System	Ext4	XFS
Kernel Version	2.6.xx	3.10.xx
Release Name	Santiago	Maipo
Gnome Version	GNOME 2	GNOME 3.8
KDE Version	KDE 4.1	KDE 4.6
Release Date	Wednesday, November 10, 2010	Tuesday, June 10, 2014
NFS Version	NFS 4	NFS 4.1. NFS V2 is deprecated in RHEL 7
Samba Version	SMB 3.6	SMB 4.4
Default Database	MySQL	MariaDB
Cluster Resource Manager	Rgmanager	Pacemaker
Network InterfaceGrouping	Bonding can be done as Active-Backup, XOR, IEEE and Load Balancing	Team Driver will support multiple types of Teaming methods called Active-Backup, Load-balancing and Broadcast
KDUMP	Kdump does't support with large RAM Size	RHEL 7 can be supported up to 3TB
Boot Loader	Grub 2 /boot/grub2/grub.cfg	Grub 0.97 /boot/grub/grub.conf
File System Check	e2fsck -Inode check. Block and size check –Directory Structure check -Directory Link Check -reference count check -Group Summary Check	xfs_replair – Inode blockmap checks -Inode allocation map checks -Inode size check -Directory check -Path Name check -Link count check -Freemap check -Super block check
Process ID	Initd  Process ID 1	Systemd Process ID 1
Port Security	Iptables by default service port is enabled when service is switched on.	Firewalld instead of iptables. Iptables can also support with RHEL 7, but we can't use both of them at the same time. Firewall will not allow any port until and unless you enabled it.
Boot Time	40 Sec	20 Sec
File System Size	EXT4 16TB with XFS 100TB	XFS 500TB with EXT4 16TB
Processor Architecture	32Bit and 64Bit	Only 64Bit.
Network Configuration Tool	setup	nmtui
Host name Config File	/etc/sysconfig/network	/etc/hostname No need to edit hostname file to write permanent hostname simply use hostnamectl command
Interface Name	eth0	ens33xxx
Managing Services	service sshd start service sshd restart chkconfig sshd on	systemctl start sshd.service systemctl restart sshd.service systemctl enable sshd.service
System Logs	/var/log/	/var/log journalctl
Run Levels	runlevel 0 – Power Off runlevel 1 – Single User Mode runlevel 2 – Multi User without Networking runlevel 3 – Multi User CLI runlevel 4 – Not USed runlevel 5 – GUI Mode runlevel 6 – Restart	There is no run levels in RHEL 7. Run levels are called as targets Poweroff.target rescue.target multi-user.target graphical.target reboot.target
UID Information	Normal User UID will start from 500 to 65534 System Users UID will start from 1 to 499	Normal User UID start from 1000 – 65534 System Users UID will start from 1 to 999Because Services are increased compare to RHEL 6
By Pass Root Password Prompt	append 1 or s or init=/bin/bash to Kernel command line	Append rd.break or init=/bin/bash to kernel command line
Rebooting and Poweroff	poweroff – init 0 reboot – init 6	systemctl poweroff systemctl reboot
YUM Commands	yum groupinstall yum groupinfo	yum group install yum group info

Features	RHEL 7	RHEL 6
Default File System	XFS	EXT4
Kernel Version	3.10.x-x kernel	2.6.x-x Kernel
Kernel Code Name	Maipo	Santiago
General Availability Date of First Major Release	2014-06-09 (Kernel Version 3.10.0-123)	2010-11-09 (Kernel Version 2.6.32-71)
First Process	systemd (process ID 1)	init (process ID 1)
Runlevel	runlevels are called as "targets" as shown below: runlevel0.target -> poweroff.target runlevel1.target -> rescue.target runlevel2.target -> multi-user.target runlevel3.target -> multi-user.target runlevel4.target -> multi-user.target runlevel5.target -> graphical.target runlevel6.target -> reboot.target /etc/systemd/system/default.target (this by default is linked to the multi-user target)	Traditional runlevels defined : runlevel 0 runlevel 1 runlevel 2 runlevel 3 runlevel 4 runlevel 5 runlevel 6 and the default runlevel would be defined in "/etc/inittab" file.
Host Name Change	In Red Hat Enterprise Linux 7, as part of the move to the new init system (systemd), the hostname variable is defined in "/etc/hostname" file.	In Red Hat Enterprise Linux 6, the hostname variable was defined in the "/etc/sysconfig/network" configuration file.
Change In UID Allocation	By default a new user created would get UIDs assigned starting from 1000. This could be changed in "/etc/login.defs" file if required.	Default UID assigned to users would start from 500. This could be changed in "/etc/login.defs" file if required.
Max Supported File Size	Maximum (individual) file size = 500TB Maximum filesystem size = 500TB (This maximum file size is only on 64-bit machines. Red Hat Enterprise Linux does not support XFS on 32-bit machines.)	Maximum (individual) file size = 16TB Maximum filesystem size = 16TB (This maximum file size is based on a 64-bit machine. On a 32-bit machine, the maximum files size is 8TB.)
File System Check	"xfs_repair" XFS does not run a file system check at boot time.	"e2fsck" File system check would gets executed at boot time.
Differences Between xfs_repair & e2fsck	"xfs_repair" - Inode and inode blockmap (addressing) checks. - Inode allocation map checks. - Inode size checks. - Directory checks. - Pathname checks. - Link count checks. - Freemap checks. - Super block checks.	"e2fsck" - Inode, block, and size checks. - Directory structure checks. - Directory connectivity checks. - Reference count checks. - Group summary info checks.
Difference Between xfs_growfs & resize2fs	"xfs_growfs" xfs_growfs takes mount point as arguments.	"resize2fs" resize2fs takes logical volume name as arguments.
Change In File System Structure	/bin, /sbin, /lib, and /lib64 are now nested under /usr.	/bin, /sbin, /lib, and /lib64 are usually under /
Boot Loader	GRUB 2 Supports GPT, additional firmware types, including BIOS, EFI and OpenFirmware. Ability to boot on various file systems (xfs, ext4, ntfs, hfs+, raid, etc)	GRUB 0.97
KDUMP	RHEL7 supports kdump on large memory based systems up to 3 TB	Kdump doesn't work properly with large RAM based systems.
System & Service Manager	"Systemd" systemd is a system and service manager for Linux, and replaces SysV and Upstart used in previous releases of Red Hat Enterprise Linux. systemd is compatible with SysV and Linux Standard Base init scripts.	Upstart
Enable/Start Service	For RHEL 7, the systemctl command replaces service and chkconfig. - Start Service : "systemctl start nfs-server.service". - Enable Service : To enable the service (example: nfs service ) to start automatically on boot : "systemctl enable nfs-server.service". Although one can still use the service and chkconfig commands to start/stop and enable/disable services, respectively, they are not 100% compatible with the RHEL 7 systemctl command	Using "service" command and "chkconfig" commands. - Start Service : "service start nfs" OR "/etc/init.d/nfs start" - Enable Service : To start with specific runlevel : "chkconfig --level 3 5 nfs on"
Default Firewall	"Firewalld (Dynamic Firewall)" The built-in configuration is located under the "/usr/lib/firewalld" directory. The configuration that you can customize is under the "/etc/firewalld" directory. It is not possible to use Firewalld and Iptables at the same time. But it is still possible to disable Firewalld and use Iptables as before.	Iptables
Network Bonding	"Team Driver" -/etc/sysconfig/network-scripts/ifcfg-team0 - DEVICE=」team0」 - DEVICETYPE=」Team」	"Bonding" -/etc/sysconfig/network-scripts/ifcfg-bond0 - DEVICE=」bond0」
Network Time Synchronization	Using Chrony suite (faster time sync compared with ntpd)	Using ntpd
NFS	NFS4.1 NFSv2 is no longer supported. Red Hat Enterprise Linux 7 supports NFSv3, NFSv4.0, and NVSv4.1 clients.	NFS4
Cluster Resource Manager	Pacemaker	Rgmanager
Load Balancer Technology	Keepalived and HAProxy	Piranha
Desktop/GUI Interface	GNOME3 and KDE 4.10	GNOME2
Default Database	MariaDB is the default implementation of MySQL in Red Hat Enterprise Linux 7	MySQL
Managing Temporary Files	RHEL 7 uses systemd-tmpfiles (more structured, and configurable, method to manage tmp files and directories).	Using "tmpwatch"