CompTIA Linux+ XK0-006 (V8) Practice Question
A production application server is still reachable by ping and continues to serve web traffic, but every new SSH attempt from the operations team fails with the message "PTY allocation request failed on channel 0" and then the connection closes. A colleague who already had an interactive shell gathers the following information:
$ systemctl status sshd
● sshd.service - OpenSSH server daemon
Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)
Active: active (running)
...
$ sudo ss -ltnp | grep :22
LISTEN 0 128 0.0.0.0:22 0.0.0.0:* users:(("sshd",pid=1389,fd=3))
$ df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/cs-root 50G 29G 19G 61% /
$ df -i /
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/mapper/cs-root 3276800 3276800 0 100% /
Based on this output, which of the following best explains why the server will not accept additional SSH logins?
The inode table on the root filesystem is full, preventing sshd from creating the pseudo-terminal device files needed for a new session.
sshd has reached its MaxSessions limit in
sshd_config, so additional logins are rejected until the service restarts.The TCP backlog queue for port 22 is full, so the kernel is silently dropping incoming SYN packets.
The kernel parameter
kernel.pty.maxis set too low, limiting the total number of pseudo-terminals to 256.