Speed Up Sysadmin Tasks: Fast File Deletion, iSCSI Detection, and Group Management

Requirements

During daily operations we often encounter scenarios such as quickly deleting large numbers of files, detecting newly added iSCSI disks in vSphere without a reboot, preventing accidental rm deletions, mounting filesystems across Linux servers rapidly, and adding users to secondary groups efficiently.

How to quickly delete massive files on Linux?

How to make vSphere recognize a newly added iSCSI disk without restarting?

How to protect rm from accidental deletions?

How to mount between different Linux servers quickly?

How to add a user to supplementary groups swiftly?

1. How to quickly delete massive files on Linux?

Using

rm

on many small files or large files can be slow and may leave disk space unreleased because each entry is unlinked individually. Replacing

rm

with

rsync

dramatically speeds up the process by swapping the directory with an empty one.

Key rsync delete options:

<code>rsync --help | grep delete
    --del                   an alias for --delete-during
    --delete                delete files that don't exist on the sending side
    --delete-before         receiver deletes before transfer (default)
    --delete-during         receiver deletes during transfer, not before
    --delete-after          receiver deletes after transfer, not before
    --delete-excluded       also delete excluded files on the receiving side
    --ignore-errors         delete even if there are I/O errors
    --max-delete=NUM        don't delete more than NUM files</code>

Fast directory deletion

<code>1. mkdir -p /del_tmp
2. Target directory to clear: /del_dest
3. rsync --delete-before -a -H -v --progress --stats ./del_tmp/ ./del_dest/</code>

Fast file deletion

Note: When source and destination types differ, errors occur; when both are files (f) the command empties the file content instead of deleting; when both are directories (d) it removes all files inside, leaving an empty directory.

2. Detecting a newly added iSCSI disk in vSphere without reboot

Two methods are provided.

Method 1

Write a command to

/proc/scsi/scsi

to add the new device (assuming it appears as “Direct‑Access”):

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

Parameters:

HOST – host adapter ID (0 is first, new disk uses 2)

Channel – SCSI channel on the host (00 for both old and new)

ID – SCSI device ID, starts at 00; new disk is 01

Method 2

<code># Refresh SCSI; repeat for each host
# If there are 3 hosts, run three times
echo "- - -" > /sys/class/scsi_host/host0/scan
echo "- - -" > /sys/class/scsi_host/host1/scan
echo "- - -" > /sys/class/scsi_host/host2/scan</code>

Either method allows the system to recognize the new disk without a reboot.

3. Preventing accidental rm deletions

Leverage Bash parameter expansion to supply a safe default when a variable is empty:

<code># Format: ${parameter:-default}
# Example command
rm -rf ${dest:-test}
# If $dest is unset or empty, the command becomes rm -rf test (safe).
# If $dest is set, it deletes the specified path.
# Improved safe version
rm -rf /${dest:-test}</code>

4. Fast mounting between Linux servers

While NFS is common,

sshfs

provides a quick SSH‑based mount.

<code># Install SSHFS
yum install sshfs
# Create mount point
mkdir /mnt/data
# Mount remote directory
sshfs [email protected]:/home/test/ /mnt/data
# With key authentication
sshfs -o IdentityFile=~/.ssh/id_rsa [email protected]:/home/test/ /mnt/data</code>

This method is simpler than configuring NFS.

5. Adding a user to supplementary groups efficiently

Using

usermod

overwrites existing groups. The

gpasswd

command can add a user to a group without needing to know current memberships.

<code># Add test1 to test2
gpasswd -a test1 test2
# Add test1 to test3
gpasswd -a test1 test3</code>

This is handy when a user must belong to multiple groups for shared file permissions.

Conclusion

Standard operations can solve most issues, but exploring alternative commands and tools can greatly improve efficiency and reduce manual effort in daily sysadmin work.