OLE common mistakes

Candidates memorize that Oracle Linux ships two kernels but never learn that UEK release strings contain 'uek' and that the default boot entry must be set with 'grubby --set-default' or by setting GRUB_DEFAULT in /etc/default/grub followed by 'grub2-mkconfig -o /boot/grub2/grub.cfg'. Manual edits are overwritten on the next kernel install, and questions probe which kernel provides btrfs, Ksplice, and newer drivers.

Ksplice is Oracle Linux-specific and heavily marketed, so candidates over-generalize: they forget it only covers kernels and a defined set of critical user-space packages, that an effective kernel must be supported, and that the client is 'ksplice-uptrack' (with ksplice support enabled through ULN or the Ksplice-aware yum repo). Questions test whether a reboot is needed and how to verify patch state.

Oracle Linux offers several repository sources (ULN, the public yum.oracle.com mirrors, and local ISO/media repos), and candidates mix them. They also forget that a system registered with ULN must have its repos enabled per system, and that 'yum-config-manager --enable' or 'dnf config-manager --set-enabled' is needed after registration. Baseurl typos and missing gpgkey settings then cause silent failures.

Candidates learn lvextend and resize2fs as separate steps but forget the order and the filesystem-specific tool. On XFS they run resize2fs (which fails, since XFS cannot shrink and uses xfs_growfs), and they forget that xfs_growfs takes a mount point while resize2fs takes a device. Questions often combine pvcreate/vgextend/lvextend into one chain.

Candidates copy device names like /dev/sdb1 from a lab, which shift after reboot, or they add NFS/extra mounts without nofail and x-systemd.automount. They also forget that a broken fstab triggers emergency mode and that the fix requires booting with rd.break or emergency.target and remounting root read-write.

Older study material and muscle memory point to the legacy network service and /etc/sysconfig/network-scripts, which are deprecated or absent on EL8/EL9. Candidates also run 'nmcli con mod' and assume it takes effect immediately, but modifying a connection does not activate it until 'nmcli con up' or a reactivate is issued.

SELinux denials look like random permission failures, so candidates reach for the off switch. They also forget that changing SELINUX=enforcing to permissive requires a reboot, that 'setenforce 0' is temporary, and that file contexts are fixed with restorecon or semanage fcontext rather than chmod. Questions test targeted fixes and denial analysis.

firewalld keeps a runtime and a permanent configuration, and candidates apply a rule, test it successfully, then lose it after reboot. Others bypass firewalld with iptables commands that firewalld later flushes. They also forget that a service must be added to the correct zone and that the default zone matters.

The format of /etc/cron.d and /etc/crontab includes a user column that user crontabs do not, and candidates copy entries between the two. They also forget cron's minimal environment, so scripts relying on PATH, aliases, or relative paths fail silently, and they miss that output goes to local mail and cron logs to /var/log/cron.

Candidates focus on the command name and skip the attributes that matter: 'useradd -m -s /bin/bash', 'passwd', supplementary groups with 'usermod -aG', and the difference between primary and supplementary groups. Permission questions test setgid directories for shared collaboration and the effect of umask 027 versus 022, which candidates rarely rehearse.