Debian tutorials - Page 2

Set SFTP upload permissions with OpenSSH internal-sftp -u in sshd_config, apply umask per user or group with Match blocks, and understand why umask removes bits but cannot add them.

Use pkill -P PARENT_PID . to send SIGTERM to every direct child of a parent process, list them with ps --ppid, and clean up script workers with pkill -P $$ . on EXIT.

Automate SFTP file transfers in Linux shell scripts using sftp batch mode with SSH keys, or password authentication with sshpass or expect when keys are not available.

Install ARPACK runtime and development packages on Ubuntu, Debian, and RHEL-family Linux from distribution repositories, verify libraries with dpkg or rpm and pkg-config, and link a sample Fortran program against …

Add a user to a supplementary group in Linux with usermod -aG, gpasswd -a, or adduser on Debian. Verify with id, apply changes with newgrp or re-login, and avoid the missing -a mistake.

Manage Linux users and groups with useradd, usermod, userdel, groupadd, primary and supplementary groups, account defaults, and ownership checks.

Configure Chrony NTP on Linux, verify time synchronization with chronyc, force clock correction, troubleshoot sync problems, and optionally serve LAN clients.

Learn the Linux boot process from UEFI or BIOS through GRUB, the kernel, initramfs, and systemd, with inspection commands and troubleshooting.

Use perf stat, perf record, and perf report on Linux to find CPU bottlenecks, collect call graphs, and resolve symbols with debuginfod on Rocky Linux, RHEL, Debian, Ubuntu, and other distributions.

Learn how to check ML-KEM support in TLS, create ML-DSA signatures, and verify post-quantum SSH key exchange on Linux, with tested Rocky Linux examples.

When a Linux VM shows the wrong time after every reboot, trace the clock from the virtual RTC through chrony, identify the selected NTP source, and fix stale RTC values, unsuitable chrony sources, or hypervisor time-sync …

Configure Apache HTTP Server to authenticate and authorize users with OpenLDAP using mod_authnz_ldap, group restrictions, TLS, and practical troubleshooting.

Fix missing Bash history commands in Linux, including commands lost across multiple terminals, delayed .bash_history writes, HISTCONTROL exclusions, and permission problems.

Create a Linux man page with a reusable groff template. Learn man sections, macros, local preview, system and user installation, mandb, whatis, and troubleshooting.

Create a system-level systemd service that starts at boot and runs as a dedicated non-root user and group on Ubuntu, Debian, Fedora, RHEL, Rocky Linux, AlmaLinux, CentOS Stream and Oracle Linux.

Restart or reload cron in Linux with systemctl restart cron on Ubuntu and Debian or crond on RHEL and Rocky Linux, and when a reload is actually needed.

Compare the RHEL and Debian Linux families, including RPM vs DEB, DNF vs APT, repositories, release models, lifecycle, security, support, configuration, cloud images and server use cases.

Learn how Unix, Linux, GNU/Linux and Linux distributions relate, why Ubuntu, Debian, Fedora, RHEL, Rocky Linux and Arch differ beyond desktop themes, and how to identify your distro from the shell.

Fix curl error 60 and similar HTTPS failures on Linux when corporate SSL inspection replaces public certificates with a private root CA trusted on Windows but missing from the Linux trust store.

Migrate an already-installed Ubuntu LVM root volume group onto a new LUKS2 physical volume with pvmove, then configure crypttab with initramfs, regenerate the initramfs, and update GRUB for boot-time unlock.

Use systemd-cryptenroll on LUKS2 volumes to add TPM2, FIDO2, PKCS#11, and recovery-key unlock methods, store token metadata in the LUKS2 JSON area, and wire boot unlock through crypttab.

Extend or shrink a LUKS2 ext4 volume on Linux: grow the partition first, run cryptsetup resize on the mapper, then resize2fs; for shrink, reverse the order with offline resize2fs and --size in 512-byte sectors.

Unlock and mount a LUKS USB or moved disk on another Linux host: cryptsetup open by device, UUID=, or /dev/disk/by-uuid, ext4 or LVM inside LUKS, read-only rescue mount, and close the mapper.

Configure crypttab and fstab to unlock and mount a secondary LUKS data partition at boot on Ubuntu or Debian.

Back up and restore a LUKS2 header with cryptsetup luksHeaderBackup and luksHeaderRestore, use a detached header file, and understand when a header copy cannot recover a forgotten passphrase.

Rotate LUKS passphrases and key slots, change cipher or volume key with cryptsetup reencrypt on LUKS2, and back up the header before destructive operations.

Encrypt a new Linux disk partition with LUKS2 using cryptsetup: partition the disk, run luksFormat, open the mapper, create ext4 on /dev/mapper, and mount the volume.

List users in Linux with getent, /etc/passwd, who, and id. Filter normal and system accounts, see logged-in sessions, and check whether a user exists on Ubuntu and RHEL.

List groups in Linux with getent, groups, id, and /etc/group. Check user group membership, list group members, and compare primary vs supplementary groups.

Import a CA or TLS certificate into Java cacerts on Ubuntu, Debian, RHEL, and Rocky Linux with keytool -importcert: locate cacerts, use a copy for safe testing, default password changeit, and distro-specific system trust …