Chapter 2. Major Changes and Migration Considerations This chapter discusses major changes and features that may affect migration from Red Hat Enterprise Linux 6 to Red Hat Enterprise Linux 7. Read each section carefully for a clear understanding of how your system will be impacted by upgrading to Red Hat Enterprise Linux 7. 2.1. System Limitations Red Hat Enterprise Linux supported system limitations have changed between version 6 and version 7. Red Hat Enterprise Linux 7 now requires at least 1 GB of disk space to install. However, Red Hat recommends a minimum of 5 GB of disk space for all supported architectures. AMD64 and Intel 64 systems now require at least 1 GB of memory to run. Red Hat recommends at least 1 GB memory per logical CPU. AMD64 and Intel 64 systems are supported up to the following limits: at most 3 TB memory (theoretical limit: 64 TB) at most 160 logical CPUs (theoretical limit: 5120 logical CPUs) 64-bit Power systems now require at least 2 GB of memory to run. They are supported up to the following limits: at most 2 TB memory (theoretical limit: 64 TB) at most 128 logical CPUs (theoretical limit: 2048 logical CPUs) IBM System z systems now require at least 1 GB of memory to run, and are theoretically capable of supporting up to the following limits: at most 3 TB memory at most 101 logical CPUs The most up to date information about Red Hat Enterprise Linux 7 requirements and limitations is available online at https://access.redhat.com/site/articles/rhel-limits . To check whether your hardware or software is certified, see https://access.redhat.com/certifications . 2.2. Installation and Boot Read this section for a summary of changes made to installation tools and processes between Red Hat Enterprise Linux 6 and Red Hat Enterprise Linux 7. 2.2.1. New Boot Loader Red Hat Enterprise Linux 7 introduces the GRUB2 boot loader, which replaces legacy GRUB in Red Hat Enterprise Linux 7.0 and later. GRUB2 supports more file systems and virtual block devices than its predecessor. It automatically scans for and configures available operating systems. The user interface has also been improved, and users have the option to skip boot loader installation. However, the move to GRUB2 also removes support for installing the boot loader to a formatted partition on BIOS machines with MBR-style partition tables. This behavior change was made because some file systems have automated optimization features that move parts of the core boot loader image, which could break the GRUB legacy boot loader. With GRUB2, the boot loader is installed in the space available between the partition table and the first partition on BIOS machines with MBR (Master Boot Record) style partition tables. BIOS machines with GPT (GUID Partition Table) style partition tables must create a special BIOS Boot Partition for the boot loader. UEFI machines continue to install the boot loader to the EFI System Partition. The recommended minimum partition sizes have also changed as a result of the new boot loader. Table 2.1, "Recommended minimum partition sizes" gives a summary of the new recommendations. Further information is available in MBR and GPT Considerations . Table 2.1. Recommended minimum partition sizes Partition BIOS & MBR BIOS & GPT UEFI & GPT /boot 500 MB / 10 GB swap At least twice the RAM. See Recommended Partitioning Scheme for details. boot loader N/A (Installed between the partition table and the first partition) Users can install GRUB2 to a formatted partition manually with the force option at the risk of causing file system damage, or use an alternative boot loader. For a list of alternative boot loaders, see the Installation Guide . If you have a dual-boot system, use GRUB2's operating system detection to automatically write a configuration file that can boot either operating system: Important Note, that if you have a dual-boot that is based on using UEFI uses other mechanism than MBR legacy based one. This means that you do not need to use EFI specific grub2 command: # grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg 2.2.1.1. Default Boot Entry for Debugging Default boot entry for systemd has been added to the /etc/grub.cfg file. It is no longer necessary to enable debugging manually. The default boot entry allows you to debug systems without affecting options at the boot time. 2.2.2. New Init System systemd is the system and service manager that replaces the SysV init system used in releases of Red Hat Enterprise Linux. systemd is the first process to start during boot, and the last process to terminate at shutdown. It coordinates the remainder of the boot process and configures the system for the user. Under systemd , interdependent programs can load in parallel, making the boot process considerably faster. systemd is largely compatible with SysV in

Commands:
grub2-mkconfig -o /boot/grub2/grub.cfg
man systemd-ask-password
rd.zfcp=0.0.4000,0x5005076300C213e9,0x5022000000000000
rd.znet=qeth,0.0.0600,0.0.0601,0.0.0602,layer2=1,portname=foo rd.znet=ctc,0.0.0600,0.0.0601,protocol=bar
rd.driver.blacklist=mod1,mod2,
rd.driver.blacklist=firewire_ohci
/dev/critical /critical xfs defaults 1 2 /dev/optional /optional xfs defaults,nofail 1 2
mv -f /var/run /var/run.runmove~ ln -sfn ../run /var/run mv -f /var/lock /var/lock.lockmove~ ln -sfn ../run/lock /var/lock
find /usr/{lib,lib64,bin,sbin} -name '.usrmove'
dmesg journalctl -ab --full
systemctl enable tmp.mount
systemctl disable tmp.mount
AUTOCREATE_SERVER_KEYS=YES export SSH_USE_STRONG_RNG=1 export OPENSSL_DISABLE_AES_NI=1
AUTOCREATE_SERVER_KEYS=YES SSH_USE_STRONG_RNG=1 OPENSSL_DISABLE_AES_NI=1
man yum
mount -o acl /dev/loop0 test mount: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so.
part /mnt/example --fstype=xfs
btrfs mount_point --data= level --metadata= level --label= label partitions
/dev/essential-disk /essential xfs auto,defaults 0 0 /dev/non-essential-disk /non-essential xfs auto,defaults,nofail 0 0
udev-alias: sdb (disk/by-id/ata-QEMU_HARDDISK_QM00001)
man ncat
undisclosed_recipients_header = To: undisclosed-recipients:;
postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply
Secret DNSBL name Name in postscreen(8) replies secret.zen.spamhaus.org zen.spamhaus.org
man rpc.nfsd
man nfs
man nfsmount.conf
systemctl start named-chroot.service
systemctl stop named-chroot.service
man keepalived.conf
man 5 votequorum
firewall-offline-cmd
yum update -y opencryptoki
pkcsconf -s pkcsconf -t
systemctl stop pkcsslotd.service
ps ax | grep pkcsslotd
cp -r /var/lib/opencryptoki/ccatok /var/lib/opencryptoki/ccatok.backup
cd /var/lib/opencryptoki/ccatok pkcscca -m v2objectsv3 -v
rm /dev/shm/var.lib.opencryptoki.ccatok
systemctl start pkcsslotd.service