The "join" utility reports: file is not sorted, but in fact it is sorted

Question

I have two files t1 and t2.

root@localhost:~#
root@localhost:~# cat t1
udp  UNCONN  0  0    0.0.0.0:68      0.0.0.0:*  users:(("dhclient",pid=479,fd=7))     479
tcp  LISTEN  0  128  127.0.0.1:6060  0.0.0.0:*  users:(("gggg-ruit",pid=24968,fd=5))  24968
root@localhost:~#
root@localhost:~# cat t2
root        88  0.0  0.0      0     0 ?        I<   Jan06   0:00 [scsi_tmf_0]
root        96  0.0  0.0      0     0 ?        I<   Jan06   0:00 [ipv6_addrconf]
root     24965  0.0  0.2  11592  3004 ?        S    Jan12   0:00 bash /root/restart_gggg.sh
root     24968  0.7  5.2 112488 53472 ?        Sl   Jan12  30:52 /usr/local/bin/gggg-ruit -singleInstance :44444

I want to join them on the 8th column of t1 and the 2nd column of t2. I already have them in sorted order. Let's prove it.

root@localhost:~# awk '{print $8}' t1
479
24968
root@localhost:~# awk '{print $2}' t2
88
96
24965
24968

Now when I join them, I got the following error.

root@localhost:~# join -1 8 -2 2 -o 2.1,2.2,1.1,1.2,1.5,1.6,2.11 t1 t2
join: t2:3: is not sorted: root     24965  0.0  0.2  11592  3004 ?        S    Jan12   0:00 bash /root/restart_gggg.sh
root@localhost:~#

Why it tells me t2 is not sorted on row 3? As you can see, it's been already sorted on the join column.

Answer 1

They’re sorted numerically, but join requires them to be sorted lexicographically: 24968, then 479; and 24965, 24968, 88, then 96.