Speed Up Linux Ops: Fast Bulk Deletion, Safe rm, Disk Refresh & User Group Tricks

1. Fast Deleting Large Files on Linux

Using rm to delete many small files or large directories is slow and may leave disk space unreleased because each entry is unlinked individually. Replacing rm with rsync dramatically speeds up the operation by swapping the target directory with an empty one.

mkdir -p /del_tmp            # create an empty directory
# target directory to clear
/del_dest
rsync --delete-before -a -H -v --progress --stats ./del_tmp/ ./del_dest/

--delete-before

: delete destination files before transfer -a: archive mode (recursive, preserve attributes) -H: preserve hard links -v: verbose output --progress: show progress --stats: display transfer statistics

2. Detect New iSCSI Disk in vSphere Without Reboot

When a new iSCSI LUN is attached to a VM, the guest OS normally requires a reboot to rescan the SCSI bus. Two command‑line methods avoid downtime.

Method 1 – Add the device via /proc/scsi/scsi

echo 'scsi add-single-device 2 0 1 0' > /proc/scsi/scsi

Parameters:

HOST : adapter number (2 in this example)

Channel : SCSI channel (0)

ID : target ID (1)

LUN : LUN number (0)

Method 2 – Rescan SCSI hosts

# Refresh each SCSI host (adjust count to your system)
for i in 0 1 2; do echo "- - -" > /sys/class/scsi_host/host${i}/scan; done

Both methods make the new disk visible without restarting the VM.

3. Making rm Safer with Bash Parameter Expansion

The Bash colon builtin can be used to provide a default value when a variable is empty, preventing accidental deletion of the root directory.

# Dangerous example (dest empty → rm -rf /)
rm -rf ${dest:-test}
# Safe version – defaults to a harmless directory
rm -rf /${dest:-test}

If dest is unset or empty, the command expands to rm -rf /test, avoiding a catastrophic rm -rf /.

4. Quick Mounting Between Linux Servers

Instead of setting up NFS, sshfs can mount a remote filesystem over SSH in a few commands.

# Install sshfs
yum install sshfs
# Create a local mount point
mkdir /mnt/data
# Mount remote directory
sshfs user@host:/home/user/ /mnt/data
# If SSH keys are configured, use the key explicitly
sshfs -o IdentityFile=~/.ssh/id_rsa user@host:/home/user/ /mnt/data

This approach is fast, requires no server‑side configuration, and works well for temporary data sharing.

5. Adding Users to Supplementary Groups Efficiently

Using usermod -G overwrites existing group memberships. The gpasswd utility adds a user to a group without affecting other groups.

# Add test1 to test2
gpasswd -a test1 test2
# Add test1 to test3
gpasswd -a test1 test3

After each command, id test1 shows the cumulative group list, eliminating the need to know the current groups beforehand.

Conclusion

By applying these straightforward commands—rsync for bulk deletion, SCSI rescanning for disk detection, Bash parameter expansion for safe rm, sshfs for rapid mounts, and gpasswd for group management—Linux system administrators can solve common operational problems more efficiently and with less risk.